Use-after-free in Exim - CVE-2026-45185
Published: May 13, 2026
Vulnerability identifier: #VU131337
CSH Severity: Critical
CVSS v4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-45185
CWE-ID: CWE-416
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to execute arbitrary code.
The vulnerability exists due to use-after-free in Exim's GnuTLS backend when handling BDAT message body transfers after a TLS close_notify alert is received before the transfer is complete. A remote attacker can send a TLS close_notify alert and then a final byte in cleartext on the same TCP connection to execute arbitrary code.
Only builds configured with USE_GNUTLS=yes are vulnerable, and exploitation requires use of the CHUNKING (BDAT) SMTP extension.
Affected software
Exim
Gentoo Linux
Ubuntu
exim4 (Ubuntu package)
mail-mta/exim
Gentoo Linux
Ubuntu
exim4 (Ubuntu package)
mail-mta/exim
How to mitigate CVE-2026-45185
Install security update from vendor's website.
Exim - update to 4.99.3
exim4 (Ubuntu package) - addressed in versions 4.82-3ubuntu2.4+esm9, 4.86.2-2ubuntu2.6+esm9, 4.90.1-1ubuntu1.10+esm6, 4.93-13ubuntu1.12+esm1
mail-mta/exim - update to 4.99.4
exim4 (Ubuntu package) - addressed in versions 4.82-3ubuntu2.4+esm9, 4.86.2-2ubuntu2.6+esm9, 4.90.1-1ubuntu1.10+esm6, 4.93-13ubuntu1.12+esm1
mail-mta/exim - update to 4.99.4