CVE-2026-40684mediumCWE-684

CVE-2026-40684: medium-severity vulnerability in Exim

Published · Updated

13Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 5.9epss 0.6%
exploitation probability
0.6%top 53% of all CVEs
observed exploitation
nono source reports it
In short

Exim email servers using musl libc can crash when receiving malformed DNS data in reverse lookup records, disrupting email delivery for that connection.

Technical detail

A vulnerability in Exim versions before 4.99.2 on musl-based systems allows remote attackers to trigger a denial of service by sending crafted DNS PTR records that exploit a dn_expand handling flaw in octal printing, causing the connection process to crash without requiring authentication.

Summary generated and translated by AI from the official description.
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 dn_expand oddity in octal printing.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
Exim · Exim
Related CVEs — Exim

In the same product, most dangerous first.

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References
https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessmenthttps://exim.org/static/doc/security/CVE-2026-40684.txthttps://www.openwall.com/lists/oss-security/2026/04/30/21http://www.openwall.com/lists/oss-security/2026/05/01/11