Bug 2493004 (CVE-2026-56123)

Summary: CVE-2026-56123 socat: Socat: Heap-based buffer overflow allows arbitrary code execution via malicious SOCKS5 proxy server
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, kshier, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, stcannon, suppawar, teagle, vlaad, watson-tool-maintainers, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in socat. A remote attacker, acting as a malicious SOCKS5 proxy server, can exploit a heap-based buffer overflow. This vulnerability, caused by a sign-extension flaw in the DOMAINNAME reply parser, allows the attacker to write arbitrary data to memory. This could lead to arbitrary code execution or a denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2535043    
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Description OSIDB Bzimport 2026-06-25 17:01:50 UTC 
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.