In Exim before 4.99.2, when JSON lookup is enabled, an out-of-bounds heap write can occur when a JSON operator encounters malformed JSON in an untrusted header, because of an incorrect implementation of \ skipping.Referenceshttps://www.openwall.com/lists/oss-security/2026/04/30/21https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessmenthttps://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57https://exim.org/static/doc/security/CVE-2026-40685.txt
