CVE-2026-40685
critical
CVSS v3
9.8
CVSS v2
—
VIR risk
9.8
Description
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.
Predictions
Exploit likelihood
97%
Patch ETA
—
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
Vendor advisory: debian — https://security-tracker.debian.org/tracker/CVE-2026-40685
Vendor advisory: cve@mitre.org — https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
Vendor advisory: cve@mitre.org — https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| debian | bookworm | fixed | 4.96-15+deb12u9 |
| debian | bullseye | affected | |
| debian | forky | fixed | 4.99.2-1 |
| debian | sid | fixed | 4.99.2-1 |
| debian | trixie | fixed | 4.98.2-1+deb13u2 |
Application impact
| Vendor | Product | Versions | Fixed |
|---|---|---|---|
| exim | exim | {"endExcluding":"4.99.2"} | 4.99.2 |
References
- https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
- https://exim.org/static/doc/security/CVE-2026-40685.txt
- https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
- https://www.openwall.com/lists/oss-security/2026/04/30/21
- https://security-tracker.debian.org/tracker/CVE-2026-40685
CWEs
CWE-684 CWE-787
Verify integrity in audit chain (admin only). AS-IS.