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.Referenceshttps://www.openwall.com/lists/oss-security/2026/04/30/21https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessmenthttps://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81https://exim.org/static/doc/security/CVE-2026-40684.txt
