Alan Coopersmith <alan.coopersmith () oracle com> writes: The common failure is accepting the sender provided length for the authentication tag, and not enforcing the minimum length specified in the RFC - allowing an attacker to specify a one-byte tag length and then use brute force to determine which of the 256 possible values matches the first byte of the actual tag. As with far too many other RFCs, the required skill for them isn't implementing them correctly, it's knowing which bits you need to ignore in order to implement them appropriately. I just checked my code and it hardcodes an allowed MAC length range of 16 ... 64 bytes for RFC 6476 use (Authenticated-Enveloped-Data, but with an explicit MAC), so no matter what any RFC says you can't feed it a MAC value less than 128 bits.
And an additional thought, these are all very high-visibility libraries and therefore obvious targets for checking whether they get it right. Given the failure rate with those, I wonder how many other lesser-known ones also got it wrong?
Peter.
https://blog.calif.io/p/how-to-format-a-ciphertext discusses how the issue that OpenSSL disclosed on June 9 as CVE-2026-34182 similarly affected the PKCS#7 / CMS parsing implementations from WolfSSL, Bouncy Castle, & GnuPG.
The common failure is accepting the sender provided length for the authentication tag, and not enforcing the minimum length specified in the RFC - allowing an attacker to specify a one-byte tag length and then use brute force to determine which of the 256 possible values matches the first byte of the actual tag.
The OpenSSL CVE-2026-34182 was already covered on oss-security in: https://www.openwall.com/lists/oss-security/2026/06/09/15
The WolfSSL CVE-2026-5500 was also already sent here in: https://www.openwall.com/lists/oss-security/2026/04/14/6
https://x.com/califio/status/2068786334844715142 notes: Both Bouncy Castle and GnuPG have acknowledged and fixed the reported issues.
CVE-2026-12802 will be published with Bouncy Castle 1.85. -- -Alan Coopersmith- alan.coopersmith () oracle com Oracle Solaris Engineering - https://blogs.oracle.com/solaris
In GnuPG before 2.5.17, a stack-based buffer overflow exists in tpm2daemon during handling of the PKDECRYPT command for TPM-backed RSA and ECC keys.
In GnuPG before 2.5.17, a long signature packet length causes parsesignature to return success with sig->data[] set to a NULL value, leading to a denial of service (application crash).
In GnuPG before 2.5.17, a stack-based buffer overflow exists in tpm2daemon during handling of the PKDECRYPT command for TPM-backed RSA and ECC keys.
In GnuPG before 2.5.17, a crafted CMS (S/MIME) EnvelopedData message carrying an oversized wrapped session key can cause a stack-based buffer overflow in gpg-agent during PKDECRYPT--kem=CMS handling. This can easily be leveraged for denial of service; however, there is also memory corruption that could lead to remote code execution.
GnuPG 2.5.17 has been released to fix a possible RCE: https://dev.gnupg.org/T8044 ("gpg-agent stack buffer overflow in pkdecrypt using KEM")
[Description for this one at the end, for the full quoted advisory.]
There's two other security-relevant bugs too: https://dev.gnupg.org/T8045 ("Stack-based buffer overflow in TPM2 PKDECRYPT") A stack-based buffer overflow exists in GnuPG’s tpm2daemon when handling the PKDECRYPT command for TPM-backed RSA and ECC keys. A local attacker who can access the daemon’s Assuan socket can send an oversized ciphertext and trigger memory corruption, resulting in a crash and potentially arbitrary code execution. When a user stores private keys inside a TPM, GnuPG runs a helper process called tpm2daemon to perform cryptographic operations on their behalf. Other GnuPG components communicate with this daemon over Assuan, a local IPC protocol. During a PKDECRYPT request, tpm2daemon copies the attacker-supplied ciphertext into fixed-size TPM work buffers without validating that the ciphertext fits. If the supplied ciphertext is larger than the TPM buffer, the copy operation writes past the end of the stack buffer and corrupts adjacent stack memory. This affects both supported TPM decrypt paths: RSA (tpm2rsadecrypt) and ECC (tpm2eccdecrypt). Because the overflow occurs on the stack and is attacker-controlled, it is potentially exploitable for code execution inside the tpm2daemon process. https://dev.gnupg.org/T8049 ("Null pointer dereference with overlong signature packet") Overlong signature packet length causes parsesignature to return success with sig->data[] left NULL, leading to a crash in later consumers. The advisory is at https://dev.gnupg.org/T7996#212268 (not yet on gnupg-announce ML). Quoting that, which discusses the main bug (T8044): These versions are affected:
GnuPG 2.5.16 (released 2025-12-30) GnuPG 2.5.15 (released 2025-12-29) GnuPG 2.5.14 (released 2025-11-19) GnuPG 2.5.13 (released 2025-10-22) Gpg4win 5.0.0 (released 2026-01-14) Gpg4win 5.0.0-beta479 (released 2026-01-02) Gpg4win 5.0.0-beta476 (released 2025-12-22) Gpg4win 5.0.0-beta395 (released 2025-10-22)
All other versions are not affected.
A crafted CMS (S/MIME) EnvelopedData message carrying an oversized wrapped session key can cause a stack buffer overflow in gpg-agent during the PKDECRYPT--kem=CMS handling. This can easily be used for a DoS but, worse, the memory corruption can very likley also be used to mount a remote code execution attack.
A CVE-id has not been assigned. We track this bug as T8044 under https://dev.gnupg.org/T8044. This vulnerability was discovered by: OpenAI Security Research. Their report was received on 2026-01-18; fixed versions released 2026-01-27.
Solution:
If an affected GnuPG version is used please update ASAP to the new version 2.5.17.
If an affected version of Gpg4win is used please update ASAP to the new version 5.0.1.
If an immediate update is not possible please remove the gpgsm or gpgsm.exe binary, this way the the bug can't be remotely triggered. sam
Hi!
On Mon, 29 Dec 2025 10:51, Werner Koch said: https://dev.gnupg.org/T7900 which is the parent ticket for all these Unfortunately this ticket and some other tickets where only accessible by registered users or even more restricted. This is now fixed [1].
FWIW, here is a replyt which I posted on Mastodon:
Actually there is only one major bug (T7906 - armor parser) which was fixed early November. T7901 requires a 2nd pre-image attack on SHA1 - which does not yet exist. T7907 (plaintext recovery) is simply untrue; see https://dev.gnupg.org/T7907#210501
BTW, of course we sign our commits and most of us even use hardware tokens.
Shalom-Salam,
Werner
[1] Phabricator has a two-level permission system and in the web interface only the first level is easy to see in the overview. Some of us played it safe and restricted at both levels. -- The pioneers of a warless world are the youth that refuse military service. - A. Einstein
Henrik Ahlgren <pablo () seestieto com> writes: Perhaps the Debian developer keyring would serve as a compelling example? They even organize actual key-signing parties, which many cryptography experts today appear to regard as "LARPing" or otherwise ridiculous. That sounds almost exactly like a CA key signing ceremony rather than any kind of WoT thing...
Peter.
Henrik Ahlgren <pablo () seestieto com> writes: Peter Gutmann <pgut001 () cs auckland ac nz> writes: Does anything actually use the cobweb of trust, or do you just assume the key you've got is good because doing anything else is too hard? Perhaps the Debian developer keyring would serve as a compelling example? They even organize actual key-signing parties, which many cryptography experts today appear to regard as "LARPing" or otherwise ridiculous. Or the Linux kernel [1].
Collin
[1] https://www.kernel.org/doc/html/v6.19-rc2/process/maintainer-pgp-guide.html#using-the-kernel-org-web-of-trust-repository
On 12/29/25 01:15, Stephan Verbücheln wrote: GnuPG follows a traditional versioning scheme where even numbers (e.g. 2.2 and 2.4) are release branches and odd numbers (2.3 and 2.5) are developer branches. So what we have to wait for is 2.4.9 fixing the vulnerabilities. Is that still true?
https://gnupg.org/ states:
Note that the 2.5 series is now declared the stable version of GnuPG. Be aware that the oldstable 2.4 series will reach end-of-life in just 6 months.
-- -Alan Coopersmith- alan.coopersmith () oracle com Oracle Solaris Engineering - https://blogs.oracle.com/solaris
Demi Marie Obenour writes: Can we agree to use OpenSSH signatures ASAP? PGP signatures are fine, for authenticating binaries we just need to use them in a way where there's only one simple, unambiguous, and minimal-attack- surface way to apply them, as well as a means of having them work over longer time periods (see below). The alternative is to try to boil the ocean, which would take a Heartbleed-style catastrophe to motivate. Interesting! Which ones don't work? I'm using it to generate test data which will no doubt trigger odd behaviour in some cases, and didn't record info about individual problems, just "type this command to get this output" once I figured out what was required. An example is:
gpg -b -z 0 --openpgp --homedir . -o signed4.pgp test.txt
(the --openpgp is for a GPG bug, without it it'll generate v3 sigs as if --force-v3-sigs had been specified).
but for most of them all I've recorded is just whatever magic incantation eventually worked to generate the required test data. Is that what gpgv and sqv are? It depends on how much of the rest of GPG is still present. If it's just a stripped-down front-end to the whole thing then it may still be subject to the same vulns. I think the hard part of doing this isn't the signature handling itself, but rather the incredibly complex web of trust. Does anything actually use the cobweb of trust, or do you just assume the key you've got is good because doing anything else is too hard? Certainly for authenticating Linux installs and updates the practice seems to be "grab the key from this source via TLS, swear a lot because it's KEYEXPIRED, spend ages Googling how to get the latest key, realise you have to install intermediate updates to work your way up to what's current but the only remaining source for those is a server in Botswana and all the apt options have changed and you need to read a garbled blog post someone wrote at 3am when they ran into the
[ 25 more lines of pain snipped ]
just run with --allow-unauthenticated and ensuing zero security so you can finally update your stuff before you die of old age". That's one thing Microsoft did well with Authenticode, you don't get all your updates blocked because your valid keys instantly became invalid after some timer ticked past midnight. I've actually done something like this myself, wrote simple apps pgpencrypt and pgpdecrypt (size around 50kB) Are these available anywhere? They're just some very quick things I threw together ten or more years ago, motivated by:
/ Used to decrypt files that the four assorted command-line versions of PGP can't handle /
(this was before GPG became the de facto universal standard). I can send you the code privately if you like, but it probably won't be very useful. Yeah, that's embarrassing. I wouldn't say it's embarrassing, more that it's a confirmation of Shamir's Law, "crypto is bypassed, not attacked". To find the biggest holes in a crypto app you need a pentester, not a cryptographer.
Peter.
On 12/29/25 11:57, Lexi Groves (49016) wrote: Hi! Thanks for the comment. Some clarifications from us: (snip) > Given a signed document, you can either check the signature or check the signature and recover the original document. To check the signature use the --verify option. To verify the signature and extract the document use the --decrypt option. The signed document to verify and recover is input and the recovered document is output. > > > > > > blake% gpg --output doc --decrypt doc.sig > > gpg: Signature made Fri Jun 4 12:02:38 1999 CDT using DSA key ID BB7576AC > > gpg: Good signature from "Alice (Judge) <alice () cyb org>" > >
We assumed that the manual was the source of truth and assumed that using --decrypt was the standard way to do this; we may have been biased here, because apparently the common knowledge about this (according to some other documentation that we did not see) was using --output/-o. However, due to the nature of the attack, setting the wrong output file while hashing the correct file, --output works the same way:
$ gpg --output x --verify msg.txt.sig msg.txt gpg: Signature made Mon 29 Dec 2025 02:59:11 PM CET gpg: using EDDSA key EE6EADB4CBB063887A3BE2B413AEBEC571BA1447 gpg: Good signature from "39c3 demo <demo () gpg fail>" [ultimate] $ cat msg.txt asdf $ cat x Malicious Does this work with 'gpgv'?
I think most software update tools use msg.txt directly and so are not vulnerable, unless the signature uses text mode in which case a different attack might work. Can you see if APT is vulnerable?
(snip) Item 5: Memory Corruption in ASCII-Armor Parsing > > This is a serious memory-safety error in GPG.
Yes. We did not have the time to try to exploit it, but we agreed that there is potential for remote code execution. We think that it is irresponsible to not release the fix on the 2.4 branch, which is what most users in the wild use. I totally agree. This is why I referred to this vulnerability as a zero-day.
(snip) Item 9: GnuPG Output Fails To Distinguish Signature Verification Success From Message Content > > I think this is actually an old problem, previously affecting Thunderbird and Git IIRC, and the existing --status-fd mechanism in GPG is meant for exactly this case, at least for automated processing.
The general concept yes, we just found that in practice --verify just does not work with encrypted and signed payloads, which further makes this harder to avoid on the CLI specifically. Also GnuPG does not fail on the first write error to the status line unless --exit-on-status-write-error is passed. Even then, some errors are not handled properly and can cause corrupt output (possibly right before an exit). -- Sincerely, Demi Marie Obenour (she/her/hers)
On 12/29/25 19:57, Peter Gutmann wrote: Stephan Verbücheln writes: The overall status is not good though. I'm more concerned about a slightly different aspect, that two researchers (apparently) walked up to GPG and quickly found a pile of bugs, many relating to authentication [0]. OpenPGP sigs are the de facto universal standard for authenticating code and binaries in the non-Windows world, the equivalent of Windows Authenticode, and GPG is the tool that's used for that. The one with all the bugs in its authentication handling. I agree. Can we agree to use OpenSSH signatures ASAP? Those actually are decently designed, though I do wish that they had the ability to include structured metadata. One could abuse the "reserved" field for this, though. Of course, it should only be parsed after verifying the signature. There are two issues that cause this, the first being that GPG is staggeringly complex. It's not a sign-and-encrypt app any more but an entire suite that runs daemons/services, spawns off subprograms, creates and uses a ton of files in its own proprietary data formats, and has a million command-line options that change across releases (I use it for generating OpenPGP test vectors so I get to try lots of options that, by the looks of it, no-one else uses because some of them function other than expected or not at all). Interesting! Which ones don't work? The second one is the format, best summed up by Thomas Ptacek's comment at https://news.ycombinator.com/item?id=46404339 which begins:
A thru-line of some of the gnarliest vulnerabilities here is PGP's insane packet system, where a PGP message is a practically arbitrary stream of packets, some control and some data, with totally incoherent cryptographic bindings. It's like something in between XMLDSIG (which pulls cryptographic control data out of random places in XML messages according to attacker- controlled tags) and SSL2 (with no coherent authentication of the complete handshake).
For an example of this, consider compressed signed data, so you've got an EDI transaction that you want to compress (it's a large blob of fixed-format text) and then sign. With CMS (Cryptographic Message Syntax) you get:
Sign( Compress( Message ) )
With OpenPGP it's a crapshoot. You'd expect something like the above but what GPG does is:
Compress( One-pass Sig || Message || Signature )
which is valid but pretty unexpected. And then any application needs to have complex and awkward logic to process these things as per tptacek's comment. Sequoia actually uses a full parser generator (LALRPOP) to deal with this.That is the only reasonable approach I know of. Incidentally, this should also be able to handle CMS just fine. The only caveat is the parser needs to be able to tell the lexer to return a single token for a certificate or CRL, and that requires an ugly lexer hack that depends on the parser not reading too many tokens ahead of time. To appreciate just how bad it really is, grab a copy of RFC 9580 and see how long it takes you to write down the sequence of fields (not packets, fields) that you'd expect to see in a message encrypted with RSA and signed with Ed25519 (to grab the two opposite ends of the cryptographic spectrum) as well as the cryptographic bindings between them, i.e. which bits get hashed/signed/ processed, and also provide a confidence level in your work. I suspect most people won't even get to that, the answer would be "I can't figure it out".
A solution for mission-critical use like authenticating downloaded binaries would be to do two things:
1. Create an app that does just that and nothing else: Here is a blob of data, here is a detached signature, is it valid for the data? Is that what gpgv and sqv are? I think the hard part of doing this isn't the signature handling itself, but rather the incredibly complex web of trust. Detached signatures seem to be the only semi-reasonable part of OpenPGP. 2. Define a fixed format for Authenticode-style signatures in OpenPGP form that allows one and only one agglutination of OpenPGP packets and fields in packets that are considered a valid signature. I actually did that myself as part of <https://github.com/QubesOS/qubes-rpm-oxide>. The OpenPGP parser built in to RPM wasn't something I wanted to expose to untrusted input, and the RPM version in Qubes OS dom0 was end of life. I added a validator that checked for the only expected format: one signature packet.
I haven't looked much into how OpenPGP encryption works and I agree that it's a much worse mess. I've actually done something like this myself, wrote simple apps pgpencrypt and pgpdecrypt (size around 50kB) that do exactly what the name says and nothing else so I don't have to remember a million command-line options and deal with a pile of files and settings. It's just "pgpencrypt file", and there's little facility to perform attacks like in the talk because there's no extra capabilities there to attack. Are these available anywhere?
(snip) [0] The talk doesn't cover how much effort was involved, the speakers mention they're not cryptographers but pen-testers so no crypto knowledge was required. Yeah, that's embarrassing. -- Sincerely, Demi Marie Obenour (she/her/hers)
In GnuPG through 2.4.8, armorfilter in g10/armor.c has two increments of an index variable where one is intended, leading to an out-of-bounds write for crafted input.
On 12/29/25 10:57, Lexi Groves (49016) wrote: Hi! Thanks for the comment. Some clarifications from us:
Item 1: Multiple Plaintext Attack on Detached PGP Signatures in GnuPG
[...] $ gpg --output x --verify msg.txt.sig msg.txt gpg: Signature made Mon 29 Dec 2025 02:59:11 PM CET gpg: Good signature from "39c3 demo <demo () gpg fail>" [ultimate] $ cat msg.txt asdf $ cat x Malicious
[...]
Item 3: Cleartext Signature Plaintext Truncated for Hash Calculation
$ gpg --export exfil () gpg fail | sq packet dump
Public-Key Packet, new CTB, 2 header bytes + 51 bytes Curve: Ed25519 Fingerprint: 06993EC337C276ECFD8C598AB613D42DB68D9E1D [...]
Signature Packet, new CTB, 3 header bytes + 371 bytes Type: DirectKey Unhashed area: Here's the zlib header! ↓
I agree that that is much more plausible.
2. Encrypt (yes, encrypt) the result of 1. with the key 3. XOR the current ciphertext with the result of 2.
Said "trampoline" does the following: So what we insert via XORing is:
This sets us up so our PGP packet stream does not get corrupted.
Clever, very clever. :-)
[...]
[...]
This logic error should still be fixed, of course. Item 13: GnuPG Trust Packet Parsing Enables Adding Arbitrary Subkeys What should be highlighted especially here are the manual page entries:
--keyring file $GNUPGHOME is used). fied keyring alone, use --keyring along with --no-default-keyring.
--import-options restore overridden.
[...]
Best, Lexi Groves (49016) -- Jacob
On 12/29/25 04:51, Werner Koch wrote: Item 5: Memory Corruption in ASCII-Armor Parsing
This is a serious memory-safety error in GPG. Yes, and actually the only serious bug from their list. This one (T7906) was fixed in the repo on November 4 (T7906) and released with 2.5.14 on 2025-11-19:
gpg: Fix possible memory corruption in the armor parser. [T7906]
and in the ExtendedLTS version 2.2.51 already on: 2025-10-28:
gpg: Fix possible memory corruption in the armor parser. [rG1e929abd20]
Another release of 2.4 is still pending but given that its end-of-life is in 6 months, it would anyway better to switch to 2.5. Whether this bug is really exploitable is still questionable but of course we decided to fix that. Thus the claim by Demi Marie "one of which allows remote code execution. [All are zero-days to the best of my knowledge.]" is over the top. Even the report marks this bug as a "may":
Impact While this may allow remote code execution (RCE), it definitively causes memory corruption.
Good research. I wasn't aware of the fix commits. The fixed bugs are indeed not zero-day vulnerabilities from an upstream perspective. They are, however, zero-day vulnerabilities for many distro users. In particular, Fedora 42, 43, and Rawhide do not have the fixes.
While upstream did use the word "may", it also states: From here it is a challenge in memory corruption exploitation with a very large space of reachable primitives. I concluded from this that exploitation is just a matter of effort. -- Sincerely, Demi Marie Obenour (she/her/hers)
Henrik Ahlgren <pablo () seestieto com> writes: "Lexi Groves (49016)" <contact () gpg fail> writes: Yes. We found this advice in The GNU Privacy Handbook, Chapter 1. Getting Started, Making and verifying signatures: I'd just like to point out that the GNU Privacy Handbook (GPH) was published in 1999, and I have not encountered any more recent revisions. I got this impression but couldn't find anything specifically saying it was archived.
I filed a bug earlier and included https://dev.gnupg.org/T7993#210212 for one issue in it, but if it's not been revised since, perhaps it should be archived with a banner on each page or something, as it's readily found via search engines at the moment. I believe GnuPG did not even support RSA until version 1.0.3 and AES/Rijndael until version 1.0.4, which were released in 2000, meaning the handbook exclusively addresses DSA and ElGamal, making it 25 years out of date. The GnuPG versions in the output got me suspicious enough ;) The GnuPG Manual (https://gnupg.org/documentation/manuals/gnupg/) is much more current, but sadly it is not structured as a user guide that would introduce a new user to PGP concepts and best practices, etc. sam
"Lexi Groves (49016)" <contact () gpg fail> writes: Yes. We found this advice in The GNU Privacy Handbook, Chapter 1. Getting Started, Making and verifying signatures: I'd just like to point out that the GNU Privacy Handbook (GPH) was published in 1999, and I have not encountered any more recent revisions. I believe GnuPG did not even support RSA until version 1.0.3 and AES/Rijndael until version 1.0.4, which were released in 2000, meaning the handbook exclusively addresses DSA and ElGamal, making it 25 years out of date.
The GnuPG Manual (https://gnupg.org/documentation/manuals/gnupg/) is much more current, but sadly it is not structured as a user guide that would introduce a new user to PGP concepts and best practices, etc.
Hi! Thanks for the comment. Some clarifications from us:
Item 1: Multiple Plaintext Attack on Detached PGP Signatures in GnuPG
> > > blake% gpg --output doc --decrypt doc.sig > gpg: Good signature from "Alice (Judge) <alice () cyb org>" > $ gpg --output x --verify msg.txt.sig msg.txt gpg: Signature made Mon 29 Dec 2025 02:59:11 PM CET gpg: using EDDSA key EE6EADB4CBB063887A3BE2B413AEBEC571BA1447 gpg: Good signature from "39c3 demo <demo () gpg fail>" [ultimate] $ cat msg.txt asdf $ cat x Malicious
Item 3: Cleartext Signature Plaintext Truncated for Hash Calculation
$ gpg --export exfil () gpg fail | sq packet dump
Public-Key Packet, new CTB, 2 header bytes + 51 bytes Curve: Ed25519 Fingerprint: 06993EC337C276ECFD8C598AB613D42DB68D9E1D [...]
Signature Packet, new CTB, 3 header bytes + 371 bytes Type: DirectKey Unhashed area: Here's the zlib header! ↓
1. Take the ciphertext of the last block, or when initializing the IV block 2. Encrypt (yes, encrypt) the result of 1. with the key 3. XOR the current ciphertext with the result of 2.
Said "trampoline" does the following: So what we insert via XORing is:
This sets us up so our PGP packet stream does not get corrupted.
GnuPG violates this in the following ways:
- "it SHOULD NOT attempt to parse nor release decrypted data to the user":
$ gpg key.gpg gpg: WARNING: no command supplied. Trying to guess what you mean ... pub ed25519 2025-12-21 [C] [expires: 2028-12-17] 7C996D1BA8E1D4082719424AE80EBABCC54F0335 uid Mallory <exfil () gpg fail> sub ed25519 2025-12-21 [S] [expires: 2028-12-17] sub cv25519 2025-12-21 [E] [expires: 2028-12-17] Item 5: Memory Corruption in ASCII-Armor Parsing This is a serious memory-safety error in GPG. Item 6: Trusted comment injection (minisign)
Agreed. This can and should be fixed.
Item 10: Cleartext Signature Forgery in GnuPG Agreed. This can and should be fixed.
Item 11: Radix64 Line-Truncation Enabling Polyglot Attacks Agreed. This can and should be fixed.
Item 13: GnuPG Trust Packet Parsing Enables Adding Arbitrary Subkeys Keyrings are trusted stores, so this is more of a documentation problem. What should be highlighted especially here are the manual page entries:
--keyring file $GNUPGHOME is used). fied keyring alone, use --keyring along with --no-default-keyring.
--import-options restore overridden. Item 14: Trusted comment Injection (minisign)
Best, Lexi Groves (49016)
Stephan Verbücheln <stephan () buecheln ch> wrote: The RCE bug was actually fixed as they already state in their slides.
https://github.com/gpg/gnupg/commit/ad0c6c33c3d6fe7ff7cc8c2e73d02ead5788e5b3 This commit seems to be related to #3 https://gpg.fail/filename while the RCE is #5 https://gpg.fail/memcpy aka CVE-2025-68973, isn't it?
cu Andreas
On Sun, Dec 28, 2025 at 9:51 PM Demi Marie Obenour <demiobenour () gmail com> wrote: On 12/28/25 05:00, Sam James wrote: Demi Marie Obenour <demiobenour () gmail com> writes: https://gpg.fail lists many vulnerabilities in GnuPG, one of which allows remote code execution.
All are zero-days to the best of my knowledge. In 2.5.14: Fedora isn't running 2.5.14 even in Rawhide. It's a zero-day for Fedora users at least.
Upstream GnuPG is increasingly unwilling to collaborate with other OpenPGP implementations, and distros are having to patch GnuPG just to restore interoperability. If possible, it would be best for distros to either outright fork the project and create a new upstream, or stop packaging GnuPG entirely in favor of Sequoia's compatibility layer. The Fedora Linux family of distributions already doesn't use GnuPG in the critical path anymore. RPM and DNF have been switched to SequoiaPGP for quite some time. That change was inherited by Red Hat Enterprise Linux 10 as well.
This is why we have PQC support in our PGP stuff.
-- 真実はいつも一つ！/ Always, there's only one truth!
Hi!
Jacob was so kind to comment on the reported bugs. I agree with most of his comments. Please let me point you also to https://dev.gnupg.org/T7900 which is the parent ticket for all these reports. We received them in October one after the other and then compiled this list of tickets.
Because there was no clear statement on when we were allowed to publish them and no further communication, most of them were set to private. I set them to public when I noticed the schedule for the talk on December 26. At that time I also drafted an article to explain the well known prblem of hard-to-correct-use of cleartext signatures including a bit of history: https://gnupg.org/blog/20251226-cleartext-signatures.html Item 5: Memory Corruption in ASCII-Armor Parsing
This is a serious memory-safety error in GPG. Yes, and actually the only serious bug from their list. This one (T7906) was fixed in the repo on November 4 (T7906) and released with 2.5.14 on 2025-11-19:
gpg: Fix possible memory corruption in the armor parser. [T7906]
and in the ExtendedLTS version 2.2.51 already on: 2025-10-28:
gpg: Fix possible memory corruption in the armor parser. [rG1e929abd20]
Another release of 2.4 is still pending but given that its end-of-life is in 6 months, it would anyway better to switch to 2.5.
Whether this bug is really exploitable is still questionable but of course we decided to fix that. Thus the claim by Demi Marie "one of which allows remote code execution. [All are zero-days to the best of my knowledge.]" is over the top. Even the report marks this bug as a "may":
Impact While this may allow remote code execution (RCE), it definitively causes memory corruption.
Good research. Item 7: Cleartext Signature Forgery in the NotDashEscaped header implementation in GnuPG
This is a misfeature that probably should not have been implemented, or should have been implemented much more strictly. Right. I did not mentioned it in my blog to keep it readable. My comment in the tcket (T7901):
I agree because the original purpose from the 90ies to enable the use of signed patch files in the Linux kernel community was never actually used and GnuPG stopped the distribution of patches from version to version many years ago. Thus I agree we should hide this option behind a compatibility flag.
This proposed flag has not yet been implemented but nevertheless the same reasoning as for all other cleartext signatures holds here. Item 12: GnuPG may downgrade digest algorithm to SHA1 during key signature checking This is T7904. The root of this is another out-of-bounds read. There is a simple fix to this: always, always, ALWAYS initialize stack-resident local variables. Which is sometimes not good because it inbits compiler checks. Anyway, good catch and was fixed on November 4. I am also unsure about the actual insecurity of SHA1 in general. Have there been more attacks since the first actual collision? For an exploit you need to have a 2nd preimage attack on SHA1 on this very data structure which has not yet been found. Item 13: GnuPG Trust Packet Parsing Enables Adding Arbitrary Subkeys That reported exploit requires social engineering to force the user to modify GnuPG local data stuctures.
Shalom-Salam,
Werner
-- The pioneers of a warless world are the youth that refuse military service. - A. Einstein
Hi,
FTR, these two got CVE assignments so far:
On Sun, Dec 28, 2025 at 12:47:30AM -0600, Jacob Bachmeyer wrote: [...] Item 3: Cleartext Signature Plaintext Truncated for Hash Calculation https://gpg.fail/formfeed
https://www.cve.org/CVERecord?id=CVE-2025-68972 Item 5: Memory Corruption in ASCII-Armor Parsing https://gpg.fail/memcpy
https://www.cve.org/CVERecord?id=CVE-2025-68973
Regards, Salvatore
In GnuPG before 2.4.9, armorfilter in g10/armor.c has two increments of an index variable where one is intended, leading to an out-of-bounds write for crafted input. (For ExtendedLTS, 2.2.51 and later are fixed versions.)
Solar Designer <solar () openwall com> writes: On Sat, Dec 27, 2025 at 07:29:53PM -0500, Demi Marie Obenour wrote: https://gpg.fail lists many vulnerabilities in GnuPG, one of which allows remote code execution. All are zero-days to the best of my knowledge. Thanks. I wish this were brought in here by the researchers, but since it was not and since we require actual content here (not just links), Indeed. I'll note that several of the vulnerability pages (say https://gpg.fail/sha1) have: Upcoming Timeline: [...] 21.12.2025: Disclosure of this report on https://seclists.org/fulldisclosure/ But I've not been able to find such a report there either.
Demi Marie Obenour <demiobenour () gmail com> writes: https://gpg.fail lists many vulnerabilities in GnuPG, one of which allows remote code execution.
All are zero-days to the best of my knowledge. In 2.5.14:
commit 115d138ba599328005c5321c0ef9f00355838ca9 Author: Werner Koch <wk () gnupg org> AuthorDate: Thu Oct 23 11:36:04 2025 +0200 Commit: Werner Koch <wk () gnupg org> CommitDate: Thu Oct 23 11:37:59 2025 +0200
gpg: Fix possible memory corruption in the armor parser.
g10/armor.c (armorfilter): Fix faulty double increment.
common/iobuf.c (underflowtarget): Assert that the filter implementations behave well. --
This fixes a bug in a code path which can only be reached with special crafted input data and would then error out at an upper layer due to corrupt input (every second byte in the buffer is unitialized garbage). No fuzzing has yet hit this case and we don't have a test case for this code path. However memory corruption can never be tolerated as it always has the protential for remode code execution.
Reported-by: 8b79fe4dd0581c1cd000e1fbecba9f39e16a396a Fixes-commit: c27c7416d5148865a513e007fb6f0a34993a6073 which fixed Fixes-commit: 7d0efec7cf5ae110c99511abc32587ff0c45b14f
In 2.5.13:
commit 8abc320f2a75d6c7339323a3cff8a8489199f49f Author: Werner Koch <wk () gnupg org> AuthorDate: Wed Oct 22 12:39:15 2025 +0200 Commit: Werner Koch <wk () gnupg org> CommitDate: Wed Oct 22 12:39:15 2025 +0200
gpg: Error out on unverified output for non-detached signatures.
g10/mainproc.c (doprocpackets): Never reset the any.data flag. --
Fixes-commit: 3b1b6f9d98b38480ba2074158fa640b881cdb97e Updates-commit: 69384568f66a48eff3968bb1714aa13925580e9f Reported-by: 8b79fe4dd0581c1cd000e1fbecba9f39e16a396a
commit 8abc320f2a75d6c7339323a3cff8a8489199f49f Author: Werner Koch <wk () gnupg org> AuthorDate: Wed Oct 22 12:39:15 2025 +0200 Commit: Werner Koch <wk () gnupg org> CommitDate: Wed Oct 22 12:39:15 2025 +0200
gpg: Error out on unverified output for non-detached signatures.
g10/mainproc.c (doprocpackets): Never reset the any.data flag.
commit db9705ef594d5a2baf0e95e13cf6170b621dfc51 Author: Werner Koch <wk () gnupg org> AuthorDate: Wed Oct 22 11:19:55 2025 +0200 Commit: Werner Koch <wk () gnupg org> CommitDate: Wed Oct 22 11:20:10 2025 +0200
gpg: Avoid potential downgrade to SHA1 in 3rd party key signatures.
But it isn't clear to me what... the mapping between all of the vulnerabilities listed on the website is vs GnuPG commits (unfortunately no CVE identifiers yet either); GnuPG bug tracker links map to commits or vulnerabilities; whether these fixes are complete for a specific vulnerability or not.
The relevant public bugs I'm aware of for GnuPG are: https://dev.gnupg.org/T7909 https://dev.gnupg.org/T7900 https://dev.gnupg.org/T7902 https://dev.gnupg.org/T7903 but some linked therein are still marked private.
Finally, to end the dump of what I know so far: Werner Koch has published a response to the cleartext signature vulnerabilities: https://gnupg.org/blog/20251226-cleartext-signatures.html.
sam
Most of them are about unreliably displaying what was actually signed and vertified.
The RCE bug was actually fixed as they already state in their slides.
https://github.com/gpg/gnupg/commit/ad0c6c33c3d6fe7ff7cc8c2e73d02ead5788e5b3
The overall status is not good though. In total (in their slides): - 1 fixed - 1 mitigated - 3 unreleased patches in Git - 7 unpatched - 2 wontfox status.
Regards
On 12/27/25 22:27, Solar Designer wrote: On Sat, Dec 27, 2025 at 07:29:53PM -0500, Demi Marie Obenour wrote: https://gpg.fail lists many vulnerabilities in GnuPG, one of which allows remote code execution. All are zero-days to the best of my knowledge. Thanks. I wish this were brought in here by the researchers, but since it was not and since we require actual content here (not just links), let me take care of this now. The website has it nicely formatted, so I also include the HTML versions, which brings the message to just below the maximum of 1 MiB here. Who knows how long this website will stay up, but oss-security archives will probably exist decades later.
The website currently says: Slides, pocs and patches soon!
"in the hurry of leaving i forgot the sites src at home, sorry, had to rewrite the whole thing. expect a nicer site by tomorrow. im patching as we speak." - crackticker (<- to blame)
1. Multiple Plaintext Attack on Detached PGP Signatures in GnuPG 2. GnuPG Accepts Path Separators and Path Traversals in Literal Data "Filename" Field 3. Cleartext Signature Plaintext Truncated for Hash Calculation 4. Encrypted message malleability checks are incorrectly enforced causing plaintext recovery attacks 5. Memory Corruption in ASCII-Armor Parsing 6. Trusted comment injection (minisign) 7. Cleartext Signature Forgery in the NotDashEscaped header implementation in GnuPG 8. OpenPGP Cleartext Signature Framework Susceptible to Format Confusion 9. GnuPG Output Fails To Distinguish Signature Verification Success From Message Content 10. Cleartext Signature Forgery in GnuPG 11. Radix64 Line-Truncation Enabling Polyglot Attacks 12. GnuPG may downgrade digest algorithm to SHA1 during key signature checking 13. GnuPG Trust Packet Parsing Enables Adding Arbitrary Subkeys 14. Trusted comment Injection (minisign) Each of the above 14 vulnerabilities has its own web page. I attach 14 text (converted with ELinks at width 80) and 14 HTML files corresponding to them.
Comments on a first reading: Item 1: Multiple Plaintext Attack on Detached PGP Signatures in GnuPG
Item 3: Cleartext Signature Plaintext Truncated for Hash Calculation
Item 5: Memory Corruption in ASCII-Armor Parsing
This is a serious memory-safety error in GPG.
Item 6: Trusted comment injection (minisign)
From Message Content
Item 10: Cleartext Signature Forgery in GnuPG Item 11: Radix64 Line-Truncation Enabling Polyglot Attacks
Item 13: GnuPG Trust Packet Parsing Enables Adding Arbitrary Subkeys
Keyrings are trusted stores, so this is more of a documentation problem. Item 14: Trusted comment Injection (minisign) -- Jacob
On Sat, Dec 27, 2025 at 07:29:53PM -0500, Demi Marie Obenour wrote: https://gpg.fail lists many vulnerabilities in GnuPG, one of which allows remote code execution. All are zero-days to the best of my knowledge. Thanks. I wish this were brought in here by the researchers, but since it was not and since we require actual content here (not just links), let me take care of this now. The website has it nicely formatted, so I also include the HTML versions, which brings the message to just below the maximum of 1 MiB here. Who knows how long this website will stay up, but oss-security archives will probably exist decades later.
The website currently says: Slides, pocs and patches soon!
"in the hurry of leaving i forgot the sites src at home, sorry, had to rewrite the whole thing. expect a nicer site by tomorrow. im patching as we speak." - crackticker (<- to blame)
1. Multiple Plaintext Attack on Detached PGP Signatures in GnuPG 2. GnuPG Accepts Path Separators and Path Traversals in Literal Data "Filename" Field 3. Cleartext Signature Plaintext Truncated for Hash Calculation 4. Encrypted message malleability checks are incorrectly enforced causing plaintext recovery attacks 5. Memory Corruption in ASCII-Armor Parsing 6. Trusted comment injection (minisign) 7. Cleartext Signature Forgery in the NotDashEscaped header implementation in GnuPG 8. OpenPGP Cleartext Signature Framework Susceptible to Format Confusion 9. GnuPG Output Fails To Distinguish Signature Verification Success From Message Content 10. Cleartext Signature Forgery in GnuPG 11. Radix64 Line-Truncation Enabling Polyglot Attacks 12. GnuPG may downgrade digest algorithm to SHA1 during key signature checking 13. GnuPG Trust Packet Parsing Enables Adding Arbitrary Subkeys 14. Trusted comment Injection (minisign) Each of the above 14 vulnerabilities has its own web page. I attach 14 text (converted with ELinks at width 80) and 14 HTML files corresponding to them.
Also included on the website is the talk video (49 minutes).
This disclosure was part of the below 39C3 talk:
https://fahrplan.events.ccc.de/congress/2025/fahrplan/event/to-sign-or-not-to-sign-practical-vulnerabilities-i To sign or not to sign: Practical vulnerabilities in GPG & friends Day 1 17:15 One en Security Dec. 27, 2025 17:15-18:15
Might contain zerodays. https://gpg.fail/ From secure communications to software updates: PGP implementations such as GnuPG ubiquitously relied on to provide cryptographic assurances. Many applications from secure communications to software updates fundamentally rely on these utilities. Since these have been developed for decades, one might expect mature codebases, a multitude of code audit reports, and extensive continuous testing. When looking into various PGP-related codebases for some personal use cases, we found these expectations not met, and discovered multiple vulnerabilities in cryptographic utilities, namely in GnuPG, Sequoia PGP, age, and minisign. The vulnerabilities have implementation bugs at their core, for example in parsing code, rather than bugs in the mathematics of the cryptography itself. A vulnerability in a parser could for example lead to a confusion about what data was actually signed, allowing attackers without the private key of the signer to swap the plain text. As we initially did not start with the intent of conducting security research, but rather were looking into understanding some internals of key management and signatures for personal use, we also discuss the process of uncovering these bugs. Furthermore, we touch on the role of the OpenPGP specification, and the disclosure process.
Beyond the underlying mathematics of cryptographic algorithms, there is a whole other layer of implementation code, assigning meaning to the processed data. For example, a signature verification operation both needs robust cryptography and assurance that the verified data is indeed the same as was passed into the signing operation. To facilitate the second part, software such as GnuPG implement parsing and processing code of a standardized format. Especially when implementing a feature rich and evolving standard, there is the risk of ambivalent specification, and classical implementation bugs.
The impact of the vulnerabilities we found reaches from various signature verification bypasses, breaking encryption in transit and encryption at rest, undermining key signatures, to exploitable memory corruption vulnerabilities.
Speakers of this event 49016 does many computer adjacent things; it has a talent for breaking them, and occasionally does security research for good in its free time.
Liam is motivated by understanding programs in depth: taking a program that runs and making it dance. Alexander