Home/CVE/In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malfor
CVE

CVE-2026-40684

In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malfor

In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dn_expand oddity in octal printing.

MEDIUM · CVSS 5.9 EPSS 0.0019
Monitor
  • No active-exploitation, high-EPSS, or public-exploit signals - routine patching cadence
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-684Incorrect Provision of Specified Functionality
▤

Affected Products & Versions

1
exim< 4.99.2
▣

Scoring & Timeline

5.9
MEDIUM · CVSS v3.1 · cve@mitre.org
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD30 Apr 2026 · 10:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
no
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
🔗

References & Sources

5
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81Patch
https://exim.org/static/doc/security/CVE-2026-40684.txtBroken Link
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessmentVendor Advisory
https://www.openwall.com/lists/oss-security/2026/04/30/21Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2026/05/01/11
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