# CVE-2026-40684

> Vulnerability · severity: **MEDIUM** (CVSS 5.9).

## 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.

## Key facts

- **CVE ID:** CVE-2026-40684
- **Published:** 2026-04-30
- **CVSS severity:** MEDIUM
- **CVSS base score:** 5.9
- **CWE codes:** CWE-684

## Affected products

- `exim:exim`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40684

## Citation

> AI Analytics. CVE-2026-40684. Retrieved 2026-07-15 from https://api.ai-analytics.org/cve/CVE-2026-40684. Derived from NIST NVD. Licensed CC0.

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