CVE-2026-40684

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 Vector

References

• https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81
• https://exim.org/static/doc/security/CVE-2026-40684.txt
• https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment
• https://www.openwall.com/lists/oss-security/2026/04/30/21