CVE-2026-56123

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.

CVSS v3 8.1 HIGH

8.1^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.2 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
http://www.dest-unreach.org/socat/CHANGES	Release Notes
https://www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser	Third Party Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:dest-unreach:socat:*:*:*:*:*:*:*:*

History

26 Jun 2026, 16:50

Type	Values Removed	Values Added
First Time		Dest-unreach socat Dest-unreach
References	~~() http://www.dest-unreach.org/socat/CHANGES -~~	() http://www.dest-unreach.org/socat/CHANGES - Release Notes
References	~~() https://www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser -~~	() https://www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser - Third Party Advisory
CPE		cpe:2.3:a:dest-unreach:socat::::::::

25 Jun 2026, 17:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-06-25 17:17

Updated : 2026-06-26 16:50

NVD link : CVE-2026-56123

Mitre link : CVE-2026-56123

CVE.ORG link : CVE-2026-56123

JSON object : View

Products Affected

dest-unreach

socat

CWE

CWE-122

Heap-based Buffer Overflow

{"id": "CVE-2026-56123", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-56123", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "version": "2.0.3", "timestamp": "2026-06-26T02:03:26.743703Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 8.1, "attackVector": "NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "HIGH", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 5.9, "exploitabilityScore": 2.2}, {"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 9.8, "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 5.9, "exploitabilityScore": 3.9}], "cvssMetricV40": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 9.2, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "valueDensity": "NOT_DEFINED", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "HIGH", "attackRequirements": "NONE", "privilegesRequired": "NONE", "subIntegrityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "affected": [{"source": "disclosure@vulncheck.com", "affectedData": [{"repo": "https://repo.or.cz/socat.git", "vendor": "socat", "product": "socat", "versions": [{"status": "affected", "version": "1.8.0.0", "lessThan": "1.8.1.2", "versionType": "custom"}], "defaultStatus": "affected"}]}], "published": "2026-06-25T17:17:01.967", "references": [{"url": "http://www.dest-unreach.org/socat/CHANGES", "tags": ["Release Notes"], "source": "disclosure@vulncheck.com"}, {"url": "https://www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser", "tags": ["Third Party Advisory"], "source": "disclosure@vulncheck.com"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "description": [{"lang": "en", "value": "CWE-122"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-06-26T16:50:16.103", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:dest-unreach:socat:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "0095DC85-1977-4C52-B3EF-F8963CDF0B41", "versionEndExcluding": "1.8.1.2", "versionStartIncluding": "1.8.0.0"}], "operator": "OR"}]}], "sourceIdentifier": "disclosure@vulncheck.com"}