# CVE-2026-40684

## Summary

- **CVE ID:** CVE-2026-40684
- **Severity:** MEDIUM
- **CVSS Score:** 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-684
- **Published:** Apr 30, 2026
- **Last Modified:** May 1, 2026

## 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.

## Affected Products

- Exim — Exim (0)

## References

- [CNA](https://exim.org/static/doc/security/CVE-2025-40684.txt)
- [CNA](https://www.openwall.com/lists/oss-security/2026/04/30/21)
- [CNA](https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment)
- [CNA](https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81)
- [CNA](https://exim.org/static/doc/security/CVE-2026-40684.txt)
- [CVE](http://www.openwall.com/lists/oss-security/2026/05/01/11)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.36%
- **EPSS Percentile:** 29.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._