CVE-2026-40684: In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when…
CVE-2026-40684 · Severity: medium · CVSS 5.9 · Published 2026-04-30
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.
No. Junglewise Threat Intelligence has no report of CVE-2026-40684 being exploited in the wild.
How severe is CVE-2026-40684?
Medium severity, with a CVSS score of 5.9, published 30 April 2026.
Which products and versions are affected?
Exim. The advisory does not name versions.
Is there a fix for CVE-2026-40684?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
Am I affected by CVE-2026-40684?
Check whether you run Exim. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.