CVE-2026-40685
critical
CVSS v3
9.8
CVSS v4 NEW
—
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
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
Debian Mixed 5 releases
| Version | Status | Fixed in |
|---|---|---|
| trixie | Fixed | 4.98.2-1+deb13u2 |
| sid | Fixed | 4.99.2-1 |
| forky | Fixed | 4.99.2-1 |
| bullseye | Affected | — |
| bookworm | Fixed | 4.96-15+deb12u9 |
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
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.