CVE-2026-40684

Denial of Service via malformed DNS PTR records exploits dn_expand bug in Exim on musl systems

Published Apr 30, 2026 CVSS 3.1 · 5.9 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DSA Debian DSA DSA-6265-1 exim4 security update
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Title Denial of Service via malformed DNS PTR records exploits dn_expand bug in Exim on musl systems
Type Values Removed Values Added
Description 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.
First Time appeared Exim
Exim exim
Weaknesses CWE-684
CPEs cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:*
Vendors & Products Exim
Exim exim
References
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
mitre
Published
Updated
May 1, 2026, 5:22 PM
Reserved
Apr 14, 2026, 12:00 AM
Status
Modified
Published
Apr 30, 2026, 10:16 PM
Modified
Nov 11, 2026, 9:10 PM