CVE-2026-40684

MEDIUMNVD 5.95.9—

5.9

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.

CVSS v3: 5.9
EG Score: 5.9(high)
EPSS: 38.6%
KEV: Not listed

Published

April 30, 2026

Last Modified

May 1, 2026

Advisory Details (3)

Auto-updated Apr 30, 2026

No patch confirmed yet.

generic

oss-security - Exim 4.99.2 fixes 4 CVEs

https://www.openwall.com/lists/oss-security/2026/04/30/21

generic

https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment

generic

Support musl libc dn_expand oddity · 628bbaca76 - exim/exim - Exim Forgejo

https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-684

Data Freshness Timeline

(refreshed 16× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-05-31 22:30 UTCepss_batch
2026-05-31 22:30 UTCepss_batch
2026-05-31 00:16 UTCepss_batch
2026-05-31 00:16 UTCepss_batch
2026-05-31 00:16 UTCepss_batch
2026-05-29 13:44 UTCepss_batch
2026-05-29 13:44 UTCepss_batch
2026-05-28 13:44 UTCepss_batch
2026-05-28 13:44 UTCepss_batch
2026-05-28 13:44 UTCepss_batch
2026-05-27 13:40 UTCepss_batch
2026-05-27 13:40 UTCepss_batch
2026-05-27 13:40 UTCepss_batch
2026-05-26 13:44 UTCepss_batch
2026-05-26 07:18 UTCepss_batch
2026-05-26 07:18 UTCepss_batch
2026-05-20 22:38 UTCepss_batch
2026-05-20 22:38 UTCepss_batch
2026-05-20 14:59 UTCEG score recompute
2026-05-20 14:59 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2026-40684?

CVE-2026-40684 is a medium vulnerability published on April 30, 2026. 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.

When was CVE-2026-40684 disclosed?

CVE-2026-40684 was first published in the National Vulnerability Database on April 30, 2026, with the most recent update on May 1, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2026-40684 actively exploited?

CVE-2026-40684 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 38.6% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2026-40684?

CVE-2026-40684 has a CVSS v3 base score of 5.9 (NVD).

How do I remediate CVE-2026-40684?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-40684, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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CVE-2026-40684

📅 Published

🔄 Last Modified

📋 Advisory Details (3)

oss-security - Exim 4.99.2 fixes 4 CVEs

Support musl libc dn_expand oddity · 628bbaca76 - exim/exim - Exim Forgejo

Weakness Classification(1)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2026-40684?

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Published

Last Modified

Advisory Details (3)

Frequently asked(5)

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