What’s Vulnerable › Vulnerabilities

CVE-2026-56123: socat 1.8.0.0 - 1.8.1.1 Heap Buffer Overflow via SOCKS5 Reply Parser

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-25 · updated 2026-06-26
• Weakness: CWE-122

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 products

• socat: from 1.8.0.0 before 1.8.1.2 — fixed in 1.8.1.2

How to fix

Upgrade to a fixed version: socat 1.8.1.2. Check the vendor advisory for mitigations.

References

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

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