# CVE-2026-40684: exim4: In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when mal...

CVE-2026-40684 is fixed in exim4 on 1 platform, first by DEBIAN-CVE-2026-40684, released May 15, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-40684
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0036
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 30, 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | exim4 Debian 12.15 (bookworm) | 4.96-15+deb12u9 | [DEBIAN-CVE-2026-40684](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40684.md) | May 15, 2026 |
| Linux | exim4 Debian 13.5 (trixie) | 4.98.2-1+deb13u2 | [DEBIAN-CVE-2026-40684](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40684.md) | May 15, 2026 |
| Linux | exim4 Debian 14 | 4.99.2-1 | [DEBIAN-CVE-2026-40684](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40684.md) | May 15, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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