# CVE-2026-56123: socat: socat versions 1.8.0.0 through 1.8.1.1 contain a heap-based buffer overflow vulnerability that allows a malicious SOC...

CVE-2026-56123 is fixed in 3 products on 1 platform, first by socat 1.8.1.1-1ubuntu0.1, released June 25, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-56123
- Priority: Urgent
- CVSS: 9.8 (critical)
- EPSS: 0.0031
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 25, 2026

## Description

socat versions 1.8.0.0 through 1.8.1.1 contain a heap-based buffer overflow vulnerability that allows a malicious SOCKS5 proxy server to overwrite adjacent heap memory by exploiting a sign-extension flaw in the DOMAINNAME reply parser. During connection setup, the domain name length byte is read through a signed char field causing a negative bytes_to_read value that is implicitly converted to size_t, resulting in an unbounded heap write into the 262-byte reply buffer with attacker-controlled size and content.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | socat Debian 13.5 (trixie) | 1.8.0.3-1+deb13u1 | [DEBIAN-CVE-2026-56123](https://patchblox.com/security/data/fix/linux/debian-cve-2026-56123.md) | Jul 3, 2026 |
| Linux | socat Debian 14 | 1.8.1.3-1 | [DEBIAN-CVE-2026-56123](https://patchblox.com/security/data/fix/linux/debian-cve-2026-56123.md) | Jul 3, 2026 |
| Linux | socat Fedora 43 | 1.8.1.3-1.fc43 | [FEDORA-2026-232FFC1325](https://patchblox.com/security/data/fix/linux/fedora-2026-232ffc1325.md) | Oct 7, 2026 |
| Linux | socat Ubuntu 24.04.5 LTS (noble) | 1.8.0.0-4ubuntu0.1 | [socat 1.8.0.0-4ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-socat-1.8.0.0-4ubuntu0.1.md) | Jul 7, 2026 |
| Linux | socat Ubuntu 26.04.1 LTS (resolute) | 1.8.1.1-1ubuntu0.1 | [socat 1.8.1.1-1ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-socat-1.8.1.1-1ubuntu0.1.md) | Jun 25, 2026 |
| Linux | socat-debuginfo Fedora 43 | 1.8.1.3-1.fc43 | [FEDORA-2026-232FFC1325](https://patchblox.com/security/data/fix/linux/fedora-2026-232ffc1325.md) | Oct 7, 2026 |
| Linux | socat-debugsource Fedora 43 | 1.8.1.3-1.fc43 | [FEDORA-2026-232FFC1325](https://patchblox.com/security/data/fix/linux/fedora-2026-232ffc1325.md) | Oct 7, 2026 |

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Data as of 2026-11-09T07:25:28Z 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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