Vulnerability · Published Jun 25, 2026 · Assigned by VulnCheck
CVE-2026-56123socat 1.8.0.0 - 1.8.1.1 Heap Buffer Overflow via SOCKS5 Reply Parser
High 8.1
In plain English
A high-severity heap buffer overflow in socat from socat. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 24% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.21 | socat | 1.8.1.2-r0 | ALPINE-CVE-2026-56123 |
| Alpine:v3.22 | socat | 1.8.1.2-r0 | ALPINE-CVE-2026-56123 |
| Alpine:v3.23 | socat | 1.8.1.2-r0 | ALPINE-CVE-2026-56123 |
| Alpine:v3.24 | socat | 1.8.1.2-r0 | ALPINE-CVE-2026-56123 |
| Debian:13 | socat | 1.8.0.3-1+deb13u1 | DEBIAN-CVE-2026-56123 |
| Debian:14 | socat | 1.8.1.3-1 | DEBIAN-CVE-2026-56123 |
| Ubuntu:24.04:LTS | socat | 1.8.0.0-4ubuntu0.1 | USN-8511-1 |
| Ubuntu:24.04:LTS | socat | 1.8.0.0-4ubuntu0.1 | UBUNTU-CVE-2026-56123 |
| Ubuntu:25.10 | socat | no fix listed | UBUNTU-CVE-2026-56123 |
| Ubuntu:26.04:LTS | socat | 1.8.1.1-1ubuntu0.1 | USN-8511-1 |
| Ubuntu:26.04:LTS | socat | 1.8.1.1-1ubuntu0.1 | UBUNTU-CVE-2026-56123 |
Affected products (as reported)
Weakness: CWE-122 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- http://www.dest-unreach.org/socat/CHANGES release-notes, patch
- https://www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser third-party-advisory