CVE-2026-56123: Dest-Unreach Socat

Critical severity, CVSS 9.8. EPSS: 0.3% chance of exploitation in the next 30 days.

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 products

• Dest-Unreach Socat: from 1.8.0.0, before 1.8.1.2 (fixed in 1.8.1.2)

Published 2026-06-25. Last modified 2026-06-26.