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9.2
CVE-2026-56123: Malicious SOCKS5 proxy can crash or hijack socat connections
CVE-2026-56123
CVE-2026-56123
Summary
Versions of socat from 1.8.0.0 to 1.8.1.1 contain a security flaw that allows a malicious proxy server to crash or take control of connections made through socat. This affects anyone using socat to connect to a SOCKS5 proxy server. Update to a fixed version of socat to protect your connections.
What to do
No fix is available yet. Check with your software vendor for updates.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| dest-unreach | socat |
>= 1.8.0.0, < 1.8.1.2 cpe:2.3:a:dest-unreach:socat:*:*:*:*:*:*:*:* |
| socat | socat | < 1.8.1.2 |
Original title
socat 1.8.0.0 - 1.8.1.1 Heap Buffer Overflow via SOCKS5 Reply Parser
Original 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.
nvd CVSS3.1
8.1
nvd CVSS4.0
9.2
Vulnerability type
CWE-122
Heap-based Buffer Overflow
Published: 25 Jun 2026 · Updated: 23 Jul 2026 · First seen: 25 Jun 2026