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Exim before 4.99.5 allows .forward privilege escalation because forcecommand for a pipe transport is mishandled.
Exim before 4.99.5 allows directory traversal to access files outside of the spool area, and consequently gain privileges, because arguments related to queue-name are mishandled.
Dear Exim users,
The Exim maintainers are releasing a security fix for two security issues.
----
Identifier: EXIM-Security-2026-06-22.1 (GCVE-25-2026-07-45-1) Type: Directory traversal, local Component: Exim Affects: 4.88 (2017) through the current 4.99.4 release Corrected in: Exim 4.99.5 (exim-4.99.5) Credit: The unnamed and uncredited authors whose works were ingested as the training corpus
Vulnerability Details ---------------------
Using command-line arguments intended for transferring queue-name through an Exim execution chain, files outside the spool area can be accessed. This can be used for a privilege escalation.
Affected Configurations -----------------------
All Exim installations; attacker with command-line access.
Mitigations -----------
None.
Resolution ----------
Upgrade to Exim 4.99.5. The fix is on branch exim-4.99+fixes, tag exim-4.99.5, signed by Jeremy Harris <jgh146exb () wizmail org>, key A986F3A6BD6377D8730958DEBCE58C8CE41F32DF.
Downloads ---------
https://ftp.exim.org/pub/exim/exim4/ https://code.exim.org/exim/exim/releases
Advisory --------
https://www.exim.org/static/doc/security/EXIM-Security-2026-06-22.1/
----
Identifier: EXIM-Security-2026-06-22.3 (GCVE-25-2026-07-45-3) Type: Command execution with alternate privilege Component: Exim Affects: 4.82 (2013) through the current 4.99.4 release Corrected in: Exim 4.99.5 (exim-4.99.5) Credit: The unnamed and uncredited authors whose works were ingested as the training corpus
Vulnerability Details ---------------------
A local user having a .forward file can use a string-expansion there. With certain Exim configurations this can be used as a privilege escalation.
Affected Configurations -----------------------
An Exim configuration with
- a redirect router implementing .forward facilities for local users - a pipe transport accessible by that router - the pipe transport having the "forcecommand" option set - the pipe transport configured to run as a privileged user
Mitigations -----------
Do not set "forcecommand" on pipe transports.
Resolution ----------
Upgrade to Exim 4.99.5. The fix is on branch exim-4.99+fixes, tag exim-4.99.5, signed by Jeremy Harris <jgh146exb () wizmail org>, key A986F3A6BD6377D8730958DEBCE58C8CE41F32DF.
Downloads ---------
https://ftp.exim.org/pub/exim/exim4/ https://code.exim.org/exim/exim/releases
Advisory --------
https://www.exim.org/static/doc/security/EXIM-Security-2026-06-22.3/
----
Timeline --------
2026-06-22 20:11 UTC Report received 2026-06-23 11:57 UTC Fix drafted 2026-07-12 12:00 UTC GCVEs assigned by GNA 2026-07-13 19:25 UTC Advance notice sent to distros () vs openwall org 2026-07-15 11:05 UTC Fix branch and tag exim-4.99.5 pushed to exim-distros 2025-07-22 14:00 UTC Public release Jeremy Harris On behalf of the Exim Maintainers
Exim 4.88 before 4.99.4, in some proxy configurations, mishandles certain short payloads, leading to disclosure of uninitialized stack memory values to a client.
Exim 4.98 before 4.98.1, when SQLite hints and ETRN serialization are used, allows remote SQL injection. (Resolving SQL injection requires an update to 4.99.1 in certain non-default rate-limit configurations.)
The STARTTLS feature in Exim through 4.94.2 allows response injection (buffering) during MTA SMTP sending.
A UNIX Symbolic Link (Symlink) Following vulnerability in the packaging of exim in openSUSE Factory allows local attackers to escalate from user mail to root. This issue affects: openSUSE Factory exim versions prior to 4.93.0.4-3.1.
Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in stringvformat in string.c involving a long EHLO command.
A flaw was found in Exim versions 4.87 to 4.91 (inclusive). Improper validation of recipient address in delivermessage() function in /src/deliver.c may lead to remote command execution.
An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1. By sending a handcrafted message, a buffer overflow may happen. This can be used to execute code remotely.
Heap-based buffer overflow in the stringvformat function in string.c in Exim before 4.70 allows remote attackers to execute arbitrary code via an SMTP session that includes two MAIL commands in conjunction with a large message containing crafted headers, leading to improper rejection logging.
Exim 4.72 and earlier allows local users to gain privileges by leveraging the ability of the exim user account to specify an alternate configuration file with a directive that contains arbitrary commands, as demonstrated by the spooldirectory directive.
Dear Exim users,
The Exim maintainers are releasing a security fix for CVE-2026-48840.
Identifier: EXIM-Security-2026-05-19.1 (CVE-2026-48840) Type: pre-authentication information disclosure Component: Exim Affects: 4.88 (2017) through the current 4.99.3 release Corrected in: Exim 4.99.4 (exim-4.99.4) Credit: Warisjeet Singh (sin99xx)
Vulnerability Details ---------------------
proxyprotocol() declares hdr as an uninitialised stack union. For a PROXYv2 frame, the only length guard is an upper bound: the frame size must not exceed sizeof(hdr). No lower bound is checked.
A frame with address family 0x21 (TCPv6) and len=0 sets the read size to 16, causing the read loop to copy exactly 0 bytes into the union. The TCPv6 dispatch arm then unconditionally calls:
memmove(tmpaddr6.sin6addr.s6addr, hdr.v2.addr.ip6.srcaddr, 16)
copying 16 uninitialised stack bytes into tmpip6, which inetntop formats as an IPv6 address string. That string is written to senderhostaddress and emitted in the SMTP greeting banner:
250 hostname Hello probe [::68ef:38ad:ffff:0]
The same defect affects family 0x11 (TCPv4) with len < 12 (4 leaked bytes instead of 16).
The leaked bytes track ASLR entropy across daemon restarts and are confirmed to be live userspace VA pointers, making this an ASLR-defeat primitive usable as a chain component.
Fix: add minimum-length checks per address family (12 bytes for TCPv4/0x11, 36 bytes for TCPv6/0x21) before the union is accessed. Frames that fail the check are rejected with proxyfail, consistent with all other malformed-frame handling in the function.
Reported by Warisjeet Singh (sin99xx). Tested on aarch64 Linux; architecture-independent (only leaked content varies).
Affected Configurations -----------------------
Exim compiled with SUPPORTPROXY (default in Debian, Ubuntu, RHEL/Fedora packages) and hostsproxy set to a non-empty value. The attacker's source IP must match hostsproxy, or the attacker must be able to reach the port that expects a PROXY header through a host already in hostsproxy.
Mitigations -----------
- Narrow hostsproxy to the exact load-balancer IPs (not a CIDR superset). - Unset hostsproxy entirely to disable PROXY-protocol parsing on the affected listener.
Resolution ----------
Upgrade to Exim 4.99.4. The fix is on branch exim-4.99+fixes, tag exim-4.99.4, signed by Heiko Schlittermann (HS12-RIPE) <hs () schlittermann de>, key 0xDD98D92359DE9E3C2663F291697F0EDD68099F6F.
Downloads ---------
https://ftp.exim.org/pub/exim/exim4/ https://code.exim.org/exim/exim/releases
Advisory --------
https://www.exim.org/static/doc/security/EXIM-Security-2026-05-19.1/
Timeline --------
2026-05-19 12:35 UTC Report received from Warisjeet Singh (sin99xx) 2026-05-19 13:26 UTC Acknowledgement sent to reporter 2026-05-19 14:06 UTC Root cause confirmed; fix drafted 2026-05-25 13:30 UTC CVE request submitted to Mitre via cveform.mitre.org 2026-05-25 17:57 UTC CVE-2026-48840 assigned by MITRE 2026-05-26 00:41 UTC Advance notice (distro-pre.txt) sent to distros () vs openwall org 2026-05-26 00:47 UTC Advance notice sent to exim-maintainers () lists exim org 2026-05-27 14:00 UTC Fix branch and tag exim-4.99.4 pushed to exim-distros 2026-05-29 14:00 UTC Public release
-- Heiko Schlittermann On behalf of the Exim Maintainers
Exim before 4.99.3, in certain GnuTLS configurations, has a remotely reachable use-after-free in the BDAT body parsing path. It is triggered when a client sends a TLS closenotify mid-body during a CHUNKING transfer, followed by a final cleartext byte on the same TCP connection. This can lead to heap corruption. An unauthenticated network attacker exploiting this vulnerability could execute arbitrary code.
Another Exim issue dropped, and this one is worth paying attention to if you still have internet-facing mail infrastructure.
CVE-2026-45185 affects Exim 4.97 through 4.99.2, but only GnuTLS builds. The bug is in BDAT message body handling and can lead to memory corruption, with potential code execution. OpenSSL builds are not affected, and the fix is in 4.99.3. The uncomfortable part is that Exim says there are no real mitigations that resolve it, so this is basically a patch situation.
What I find interesting here is not just the bug itself. It is how often old, boring infrastructure like MTAs still ends up being a high-value attack surface.
Mail servers sit exposed, handle weird protocol edge cases, process untrusted input all day, and often run in environments where nobody wants to touch them unless mail breaks.
I was thinking, how teams here are handling Exim/Postfix/etc. in 2026.
You guys are still running your own mail stack, or has this kind of recurring MTA risk pushed you fully toward managed email infrastructure?
Exim before 4.87.1 might allow remote attackers to obtain the private DKIM signing key via vectors related to log files and bounce messages.
Heiko Schlittermann <hs () nodmarc schlittermann de> writes: Hello,
The Exim maintainers are releasing an important security update to address a critical vulnerability affecting certain Exim configurations.
Vulnerability Details
A remotely reachable Use-After-Free (UAF) vulnerability has been identified in Exim's BDAT (binary data transmission) body parsing path when using the GnuTLS backend. This vulnerability can lead to heap corruption and potential code execution.
Affected Versions and Configurations
This vulnerability affects Exim versions 4.97 through 4.99.x that: - Are built with GnuTLS support - Have STARTTLS and CHUNKING advertised
Recommended Action
We strongly recommend all affected users upgrade to Exim 4.99.3 or later immediately.
Obtaining the Fix
Fixed versions are available: - Repository: https://code.exim.org/exim-/exim (branch: exim-4.99+fixes, tag: exim-4.99.3) (signed by me) - Tarballs: https://downloads.exim.org/exim4/ (signed by me) - Please see the Exim website for detailed upgrade instructions
Additional Information
- Distros already have coordinated access to patches - Internal tracking ID: EXIM-Security-2026-05-01.1 - Full technical details will be available: https://exim.org/static/doc/security/EXIM-Security-2026-05-01.1/ CVE is CVE-2026-45185. Thank you for your cooperation. And special thanks to the reporter at xbow security. Writeup at https://xbow.com/blog/dead-letter-cve-2026-45185-xbow-found-rce-exim Best regards from Dresden/Germany Viele Grüße aus Dresden Heiko Schlittermann
Heiko Schlittermann <hs () nodmarc schlittermann de> (Di 12 Mai 2026 16:15:03 CEST): - Repository: https://code.exim.org/exim-/exim (branch: exim-4.99+fixes, tag: exim-4.99.3) (signed by me) There was a typo.
Repository: https://code.exim.org/exim/exim (branch: exim-4.99+fixes, tag: exim-4.99.3) (signed by me) https://code.exim.org/exim/exim/releases/tag/exim-4.99.3 (signed by me)
Best regards from Dresden/Germany Viele Grüße aus Dresden Heiko Schlittermann -- SCHLITTERMANN.de ---------------------------- internet & unix support - Heiko Schlittermann, Dipl.-Ing. (TU) fon +49.351.8029981 - gnupg encrypted messages are welcome --------------- key ID: F69376CE -
Hello,
The Exim maintainers are releasing an important security update to address a critical vulnerability affecting certain Exim configurations.
Vulnerability Details
A remotely reachable Use-After-Free (UAF) vulnerability has been identified in Exim's BDAT (binary data transmission) body parsing path when using the GnuTLS backend. This vulnerability can lead to heap corruption and potential code execution.
Affected Versions and Configurations
This vulnerability affects Exim versions 4.97 through 4.99.x that: - Are built with GnuTLS support - Have STARTTLS and CHUNKING advertised
Recommended Action
We strongly recommend all affected users upgrade to Exim 4.99.3 or later immediately.
Obtaining the Fix
Fixed versions are available: - Repository: https://code.exim.org/exim-/exim (branch: exim-4.99+fixes, tag: exim-4.99.3) (signed by me) - Tarballs: https://downloads.exim.org/exim4/ (signed by me) - Please see the Exim website for detailed upgrade instructions
Additional Information
- Distros already have coordinated access to patches - Internal tracking ID: EXIM-Security-2026-05-01.1 - Full technical details will be available: https://exim.org/static/doc/security/EXIM-Security-2026-05-01.1/
Thank you for your cooperation. And special thanks to the reporter at xbow security.
Best regards from Dresden/Germany Viele Grüße aus Dresden Heiko Schlittermann -- SCHLITTERMANN.de ---------------------------- internet & unix support - Heiko Schlittermann, Dipl.-Ing. (TU) fon +49.351.8029981 - gnupg encrypted messages are welcome --------------- key ID: F69376CE -
In Exim before 4.99.2, when the SPA authentication driver is used with an adversarial SPA resource, there can be an out-of-bounds write that crashes the connection instance, or erroneous data processing that divulges data from uninitialized heap memory.
In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dnexpand oddity in octal printing.
In Exim before 4.99.2, when JSON lookup is enabled, an out-of-bounds heap write can occur when a JSON operator encounters malformed JSON in an untrusted header, because of an incorrect implementation of \ skipping.
In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malformed UTF-8 header data). Information might be divulged within an error message produced during handling of an unrelated e-mail message.
Solar Designer: From: Bernard Quatermass <bernardq () exim org> Subject: Re: [vs-plain] EXIM-Security-2026-04-24 To: "Distros @ oss-security openwall" <distros () vs openwall org> CC: "security () exim org" <security () exim org> Date: Wed, 29 Apr 2026 13:19:42 +0100 (2 days, 3 hours, 26 seconds ago)
we are pleased to announce the availability of release 4.99.2 of Exim.
This is a security release.
It fixes the following vulnerabilities.
CVE-2026-40684 Possible crash with malicious DNS data when using musl libc
On systems using musl libc (not glibc) due to an oddity in octal printing it is possible to crash the connection instance when malformed DNS data is present in PTR records. I sent a note to Rich Felker (musl maintainer) regarding this.
Bernard helpfully notified distros of this upcoming security release on April 24 and then of the release itself on April 29, but unfortunately did not bring this to oss-security as expected - so I am doing it now, delayed by one day.
This was also sent to the public exim-announce list yesterday:
https://lists.exim.org/lurker/message/20260429.121733.f58d9686.en.html
but it isn't prominently visible on the Exim website now. I tried clicking the Security link in the navigation on top, but this merely opened a directory listing with some text files and subdirectories in there, with all file timestamps showing as 30-Apr-2026 10:29 and so nothing clearly standing out as new. Looks like something to improve.
----- Forwarded message from Bernard Quatermass <bernardq () exim org> -----
From: Bernard Quatermass <bernardq () exim org> To: "Distros @ oss-security openwall" <distros () vs openwall org> Subject: Re: [vs-plain] EXIM-Security-2026-04-24 CC: "security () exim org" <security () exim org> Date: Wed, 29 Apr 2026 13:19:42 +0100
we are pleased to announce the availability of release 4.99.2 of Exim.
This is a security release.
It fixes the following vulnerabilities.
CVE-2026-40684 Possible crash with malicious DNS data when using musl libc
On systems using musl libc (not glibc) due to an oddity in octal printing it is possible to crash the connection instance when malformed DNS data is present in PTR records.
CVE-2026-40685 Possible OOB read/write on corrupt JSON in header
configurations using json operators on invalid externally-provided input could trigger heap corruption.
CVE-2026-40686 Possible OOB read with large UTF8 trailing characters
configurations using utf8 operators on malformed utf8 in headers could trigger OOB reads and might trigger some data leak if error messages are required for subsequent emails in the current connection and similar malformed headers are present.
CVE-2026-40687 Possible OOB read/write with SPA authenticator
in configurations using the SPA authentication driver to a hostile/compromised external SPA/NTLM connnection it is possible to trigger an OOB read/write and crash the connection instance or possibly leak heap data to the instance.
Older Exim versions may or may not be vulnerable but are not actively maintained.
We would like to thank the thousands of unnamed and uncredited authors whose works were ingested into the slopbots to "assist" in the reports for these vulnerabilities.
Exim 4.99.2 is available:
as tarball https://ftp.exim.org/pub/exim/exim4/ https://code.exim.org/exim/exim/releases
directly from Git: https://code.exim.org/exim/exim tag: exim-4.99.2
The signatures on the release tarballs should be
key ID 0xBCE58C8CE41F32DF Email: jgh () exim org
-- Bernard Quatermass
----- End forwarded message -----
Dan Rosenberg reported that when exim is used with a world-writable mail directory, with the sticky-bit set, local users could create hard-links to other non-root users' files in the mailbox storage directory, causing files to be overwritten upon mail delivery. This could be used to create a denial of service condition or potentially escalate privileges to those of targeted users.
Further information is available from the upstream bug report [1] and this has been fixed upstream in exim 4.72 [2].
[1] http://bugs.exim.org/showbug.cgi?id=988 [2] http://vcs.exim.org/viewvc/exim/exim-src/src/transports/appendfile.c?r1=1.24&r2=1.25
The /var/spool/mail directory on Red Hat Enterprise Linux and Fedora is mode 0755 and owned root:mail. As a result, this is not exploitable by default.
Dan Rosenberg reported that when MBX locking is enabled in exim, local users could exploit a race condition to change permissions of other non-root users' files. This could lead to a denial of service, to create new files owned by other users in unauthorized locations, or to possibly escalate privileges.
Further information is available from the upstream bug report [1] and this has been fixed upstream in exim 4.72 [2].
[1] http://bugs.exim.org/showbug.cgi?id=989 [2] http://vcs.exim.org/viewvc/exim/exim-src/src/transports/appendfile.c?r1=1.25&r2=1.26
While exim is built to support the MBX format, it is not the default for local mail delivery (Unix mailbox support is the default). This will only affect users that use the "mbxformat" option in the appendfile transport.
Exim before 4.99.1, with certain non-default rate-limit configurations, allows a remote heap-based buffer overflow because database records are cast directly to internal structures without validation.
According to our previous CRD announcement we released Exim 4.99.1 on 2025-12-17 at 15:00 UTC.
Credits to Andrew Fasano <andrew.fasano () nist gov>, for pointing out the issue.
His original report can be found here: https://code.exim.org/exim/exim/src/commit/d46a6727798fc48d1756190a6d46d19216348c25/doc/doc-txt/exim-security-2025-12-09.1/report.txt
Short version: Exim configurations using SQLite lookups or using SQLite hint dbs where vulnerable to SQL injection attacks, which could lead to heap corruption. Distro Exim packages usually do not use SQLite hint dbs (It is a build time option. Grep the output of exim -bV for "Hints DB".) But many packages allow SQLite lookups in the runtime config (Grep the output of exim -bV for "Lookups".)
The original release announcement, as sent to exim-announce () lists exim org: --------------------------------------------------------------------------
Dear Exim users and maintainers,
we are pleased to announce the availability of release 4.99.1 of Exim.
This is a security release. It fixes CVE-2025-67896 (aka EXIM-Security-2025-12-09.1), which was introduced with 4.99. Older Exim versions may or may not be vulnerable and are not activly maintained anymore by the Exim maintainers. (To the best of our knowledge, 4.98.2¹ should be safe.)
Configurations using SQlite for lookups and hintdb were vulnerable. Details: https://code.exim.org/exim/exim/src/branch/exim-4.99+fixes/doc/doc-txt/exim-security-2025-12-09.1/report.txt
Exim 4.99.1 is available:
as tarball https://ftp.exim.org/pub/exim/exim4/ https://code.exim.org/exim/exim/releases
directly from Git: https://code.exim.org/exim/exim tag: exim-4.99.1
The signatures on the release tarballs and Git tag should be
The release files are signed by key DD98D92359DE9E3C2663F291697F0EDD680= 99F6F "Heiko Schlittermann (Dresden) <hs () schlittermann de>" aka "Heiko Schlittermann (Exim MTA Maintainer) <heiko () exim org>"
¹) The original announcement mentioned a wrong version number.
Best regards from Dresden/Germany Viele Grüße aus Dresden Heiko Schlittermann -- SCHLITTERMANN.de ---------------------------- internet & unix support - Heiko Schlittermann, Dipl.-Ing. (TU) - {fon,fax}: +49.351.802998{1,3} - gnupg encrypted messages are welcome --------------- key ID: F69376CE -