CVE-2026-56123

socat 1.8.0.0 - 1.8.1.1 Heap Buffer Overflow via SOCKS5 Reply Parser

Published Jun 25, 2026 CVSS 4.0 · 9.2 Critical EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8511-1 socat vulnerabilities
History
Type Values Removed Values Added
First Time appeared Dest-unreach
Dest-unreach socat
CPEs cpe:2.3:a:dest-unreach:socat:*:*:*:*:*:*:*:*
Vendors & Products Dest-unreach
Dest-unreach socat
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Socat
Socat socat
Vendors & Products Socat
Socat socat
Type Values Removed Values Added
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.
Title socat 1.8.0.0 - 1.8.1.1 Heap Buffer Overflow via SOCKS5 Reply Parser
Weaknesses CWE-122
References
Metrics cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}

cvssV4_0

{'score': 9.2, 'vector': 'CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
VulnCheck
Published
Updated
Jul 14, 2026, 9:34 PM
Reserved
Jun 18, 2026, 7:15 PM
Status
Analyzed
Published
Jun 25, 2026, 5:17 PM
Modified
Jun 26, 2026, 4:50 PM