CVE-2026-45185: Exim BDAT use-after-free allows unauthenticated remote code execution
Exim 4.97 through 4.99.2 built with GnuTLS (USE_GNUTLS=yes) frees its TLS buffer when a client sends a TLS close_notify in the middle of a BDAT (CHUNKING) transfer, then keeps writing into it if one more cleartext byte follows. An unauthenticated attacker who can open a TLS SMTP session can corrupt the heap and, per the Exim advisory (CVSS 9.8) and the XBOW research, execute code. GnuTLS is the TLS library used by the Debian and Ubuntu exim4 packages; builds using OpenSSL are not affected.
- CVE-2026-45185CVE identifier
- 9.8CVSS 3.1 base score (critical)
- 1.3%EPSS: chance of exploitation in the next 30 days (higher than 70% of CVEs)
- 2026-05-12published
What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms
What to do now
- Check whether you run the affected software and which version (commands below).
- Install the fixed version for your system: see “Patch it” below.
- Restart the Exim daemon (systemctl restart exim4 on Debian/Ubuntu, exim on most other systems) so the listener runs the new binary.
- If you cannot patch today, apply the temporary mitigation below and patch as soon as possible.
Affected and fixed versions
Affected:
- Exim 4.97 up to and including 4.99.2, GnuTLS builds only
Fixed in:
- Exim 4.99.3
Am I affected?
exim -bV | head -1
exim -bV | grep -i -E 'gnutls|openssl'
dpkg -l 'exim4*' | grep ^iiPatch it
Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.
Debian
sudo apt update
sudo apt install --only-upgrade exim4-base exim4-daemon-light exim4-daemon-heavy
sudo systemctl restart exim4Ubuntu
sudo apt update
sudo apt install --only-upgrade exim4-base exim4-daemon-light exim4-daemon-heavy
sudo systemctl restart exim4Built from source
Build and install Exim 4.99.3 or later from https://ftp.exim.org/pub/exim/exim4/ and restart the daemon.General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.
Fix status in Linux distributions
| Release | Package | Status | Fixed version / advisory |
|---|---|---|---|
| Debian 12 | exim4 | fixed | 4.96-15+deb12u9 |
| Debian 13 | exim4 | fixed | 4.98.2-1+deb13u2 |
| Debian testing | exim4 | fixed | 4.99.2-2 |
| Debian 13 (trixie) | exim4 | fixed | 4.98.2-1+deb13u2 (DSA-6265-1) |
| Debian 12 (bookworm) | exim4 | fixed | 4.96-15+deb12u9 (DSA-6265-1) |
| Ubuntu 26.04 LTS (resolute) | exim4 | fixed | 4.99.1-1ubuntu1.2 (USN-8382-1) |
| Ubuntu 24.04 LTS (noble) | exim4 | fixed | 4.97-4ubuntu4.5 (USN-8382-1) |
| Ubuntu 22.04 LTS (jammy) | exim4 | fixed | 4.95-4ubuntu2.8 (USN-8382-1) |
From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.
If you cannot patch yet
- The Exim maintainers state there is no known mitigation other than upgrading.
- Builds that use OpenSSL instead of GnuTLS are not affected; check with: exim -bV
Sources
- Exim Security Advisory EXIM-Security-2026-05-01.1 / CVE-2026-45185
- CVE record CVE-2026-45185
- XBOW: Dead Letter - CVE-2026-45185 RCE in Exim
- oss-security announcement
- Debian security tracker
- Ubuntu USN-8382-1
- Ubuntu CVE page
- https://exim.org
- https://code.exim.org/exim/wiki/wiki/EximSecurity
- https://exim.org/static/doc/security/CVE-2026-45185.txt
- https://news.ycombinator.com/item?id=48111748
- https://exim.org/static/doc/security/EXIM-Security-2026-05-01.1/
- CVE-2026-45185 on NVD
Page generated automatically from official sources on 2026-11-03 18:05 UTC and reviewed by an editor. Always confirm with your vendor's advisory.