CVE-2026-40685 Memory corruption in Exim
An out-of-bounds heap write in Exim's JSON lookup allows attackers to execute code or cause denial of service via malformed headers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40685?
CVE-2026-40685 is a medium-severity memory corruption vulnerability in Exim Exim, published on 30 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-40685?
It affects 1 product.
Products include Exim Exim.
How do I fix CVE-2026-40685?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-40685 being exploited?
There is no known exploitation of CVE-2026-40685 in the wild and no public exploit code.
Other vulnerabilities in Exim Exim
Sources
Also known as CLSA-2026-1778147239, CLSA-2026-1778147777, CLSA-2026-1778690104, DEBIAN-CVE-2026-40685, GHSA-pph6-fvmv-fjrc, UBUNTU-CVE-2026-40685.