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Fencer Vulns
medium 6.5

CVE-2026-40685 json

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…

published 2026-04-30 6 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-26443

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 25%
public exploits
0
none known

Summary

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.

Patch / fix

  • Exim Exim 4.99.2
  • exim4 Debian 12 4.96-15+deb12u9
  • exim4 Debian 13 4.98.2-1+deb13u2
  • exim4 Debian 14 4.99.2-1

debian advisories DEBIAN-CVE-2026-40685

  • exim4 Ubuntu 22.04 LTS 4.95-4ubuntu2.7
  • exim4 Ubuntu 24.04 LTS 4.97-4ubuntu4.4
  • exim4 Ubuntu 25.10 4.98.2-1ubuntu2.1
  • exim4 Ubuntu 26.04 LTS 4.99.1-1ubuntu1.1
  • exim4 Ubuntu Pro 20.04 LTS 4.93-13ubuntu1.12+esm1

ubuntu advisories UBUNTU-CVE-2026-40685

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • exim Alpine 3.24, Alpine 3.23 4.98.2-r0

alpine advisories ALPINE-CVE-2026-40685

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-40685 updated cvss 6.5

Exim: Exim: Denial of Service due to malformed JSON processing

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Exim Exim

Classification

Weakness
  • CWE-684 Incorrect Provision of Specified Functionality
  • CWE-787 Out-of-bounds Write

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.