CVE-2026-56123

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.

CVSS Metrics

• v4.0•CRITICAL•Score: 9.2CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
• v3.1•HIGH•Score: 8.1CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Techniques & Countermeasures

• CWE-122•Heap-based Buffer Overflow

  A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().

Affected Systems

• socat•socat

  ≥ 1.8.0.0, < 1.8.1.2

References (2)

• http://www.dest-unreach.org/socat/CHANGES
• https://www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser