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NVD 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.
Happy to share that a vulnerability I discovered in Socat has been fixed and assigned CVE-2026-56123.
The vulnerability has a CVSS score of 9.2 and is a heap buffer overflow in the SOCKS5 reply parser.
#CyberSecurity#CVE#VulnerabilityResearch#OpenSource#Socat https://t.co/Ah4w8LRCgV
Post summary
The user announces the discovery and fix of a high‑severity heap buffer overflow in Socat’s SOCKS5 reply parser (CVE‑2026‑56123), providing CVSS score and flaw type, but offers no PoC, exploit, real‑world usage, or patch details.
🚨 HIGH - socat SOCKS5 DOMAINNAME reply heap overflow (CVE-2026-56123)
socat contains a heap-based buffer overflow in its SOCKS5 DOMAINNAME reply parser during proxy connection setup. The root cause is a sign-extension flaw where a negative length is converted to size_t, resulting in improper bounds checking and an out-of-bounds heap write into a fixed 262-byte reply buffer. An attacker can exploit this by operating or intercepting a SOCKS5 proxy server and returning a crafted DOMAINNAME reply that triggers the negative length and forces socat to copy attacker-controlled data past the heap buffer, typically without needing local privileges beyond getting the victim to use that proxy. Impact ranges from process crash/denial of service to potential remote code execution via heap corruption, depending on allocator behavior and runtime mitigations.
👉 Affected: socat 1.8.0.0 through 1.8.1.1 | Upgrade to No fix yet - treat as suspicious
Post summary
The post announces a heap-based buffer overflow in socat’s SOCKS5 domain name reply parser, detailing the technical mechanism and potential impact, but offers no PoC, exploit code, or known active exploitation.
