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.
A bug found in libksba, the library used by GnuPG for parsing the ASN.1 structures as used by S/MIME. The bug affects all versions of Libksba before 1.6.2 and may be used for remote code execution.
https://www.gnupg.org/blog/20221017-pepe-left-the-ksba.html https://dev.gnupg.org/T6230 https://dev.gnupg.org/rK4b7d9cd4a018898d7714ce06f3faf2626c14582b https://lwn.net/Articles/911467/
GnuPG version 2.1.12 - 2.2.11 contains a Cross ite Request Forgery (CSRF) vulnerability in dirmngr that can result in Attacker controlled CSRF, Information Disclosure, DoS. This attack appear to be exploitable via Victim must perform a WKD request, e.g. enter an email address in the composer window of Thunderbird/Enigmail. This vulnerability appears to have been fixed in after commit 4a4bb874f63741026bd26264c43bb32b1099f060.
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 2.4.9, 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.)
GnuPG before version 2.2.8 does not properly sanitize original filenames of signed or encrypted messages allowing for the insertion of line feeds and other control characters. An attacker could exploit this by injecting such characters to craft status messages and fake the validity of signatures.
External Reference:
https://lists.gnupg.org/pipermail/gnupg-announce/2018q2/000425.html
Upstream Issue:
https://dev.gnupg.org/T4012
Upstream Patches:
https://dev.gnupg.org/rG2326851c60793653069494379b16d84e4c10a0ac https://dev.gnupg.org/rG210e402acd3e284b32db1901e43bf1470e659e49 https://dev.gnupg.org/rG13f135c7a252cc46cff96e75968d92b6dc8dce1b
GnuPG 2.2.4 and 2.2.5 does not enforce a configuration in which key certification requires an offline master Certify key, which results in apparently valid certifications that occurred only with access to a signing subkey.
A flaw was found in the way certificate signatures could be forged using collisions found in the SHA-1 algorithm. An attacker could use this weakness to create forged certificate signatures. This issue affects GnuPG versions before 2.2.18.
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.
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.
Heap-based buffer overflow in the askoutfilename function in openfile.c for GnuPG (gpg) 1.4 and 2.0, when running interactively, might allow attackers to execute arbitrary code via messages with "C-escape" expansions, which cause the makeprintablestring function to return a longer string than expected while constructing a prompt.
In GnuPG through 2.4.8, if a signed message has \f at the end of a plaintext line, an adversary can construct a modified message that places additional text after the signed material, such that signature verification of the modified message succeeds (although an "invalid armor" message is printed during verification). This is related to use of \f as a marker to denote truncation of a long plaintext line.
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).
The integrity check feature in OpenPGP, when handling a message that was encrypted using cipher feedback (CFB) mode, allows remote attackers to recover part of the plaintext via a chosen-ciphertext attack when the first 2 bytes of a message block are known, and an oracle or other mechanism is available to determine whether an integrity check failed.
parse-packet.c in GnuPG (gpg) 1.4.3 and 1.9.20, and earlier versions, allows remote attackers to cause a denial of service (gpg crash) and possibly overwrite memory via a message packet with a large length (long user ID string), which could lead to an integer overflow, as demonstrated using the --no-armor option.
Integer overflow in parsecomment in GnuPG (gpg) 1.4.4 allows remote attackers to cause a denial of service (segmentation fault) via a crafted message.
GnuPG 1.4.6 and earlier and GPGME before 1.1.4, when run from the command line, does not visually distinguish signed and unsigned portions of OpenPGP messages with multiple components, which might allow remote attackers to forge the contents of a message without detection.
In GnuPG before 2.5.5, if a user chooses to import a certificate with certain crafted subkey data that lacks a valid backsig or that has incorrect usage flags, the user loses the ability to verify signatures made from certain other signing keys, aka a "verification DoS."
USN-3675-1 fixed a vulnerability in GnuPG 2 for Ubuntu 18.04 LTS and Ubuntu 17.10. This update provides the corresponding update for GnuPG 2 in Ubuntu 16.04 LTS and Ubuntu 14.04 LTS. Original advisory details: Marcus Brinkmann discovered that during decryption or verification, GnuPG did not properly filter out terminal sequences when reporting the original filename. An attacker could use this to specially craft a file that would cause an application parsing GnuPG output to incorrectly interpret the status of the cryptographic operation reported by GnuPG.
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. -- Sincerely, Demi Marie Obenour (she/her/hers)
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
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
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
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
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.
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
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
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! 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