Vulnerability Details CVE-2026-56123
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 23.1%
CVSS Severity
CVSS v3 Score 8.1
References
Products affected by CVE-2026-56123
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cpe:2.3:a:dest-unreach:socat:1.8.0.0
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cpe:2.3:a:dest-unreach:socat:1.8.0.1
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cpe:2.3:a:dest-unreach:socat:1.8.0.2
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cpe:2.3:a:dest-unreach:socat:1.8.0.3
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cpe:2.3:a:dest-unreach:socat:1.8.1.0
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cpe:2.3:a:dest-unreach:socat:1.8.1.1