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Vulnerability record · CVE-2026-56123 · published 25 June 2026

CVE-2026-56123: Dest-unreach socat heap-based buffer overflow vulnerability

DDest Unreach · Socat

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.

9.2 CVSS 4.0 Critical EPSS 0.55% · top 56.3% CWE-122 · Heap-based buffer overflow
9.2CVSS 4.0 base score
0.55%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
26 Jun 2026Last modified by 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.

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:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
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

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.5CVE-2015-1379Dest-unreach socat improper input validation vulnerabilityThe signal handler implementations in socat before 1.7.3.0 and 2.0.0-b8 allow remote attackers to cause a denial of service (process freeze or crash).EPSS 3.9%6.8CVE-2010-2799Dest-unreach socat memory buffer overflow vulnerabilityStack-based buffer overflow in the nestlex function in nestlex.c in Socat 1.5.0.0 through 1.7.1.2 and 2.0.0-b1 through 2.0.0-b3, when bidirectional d…EPSS 2.8%6.2CVE-2012-0219Dest-unreach socat memory buffer overflow vulnerabilityHeap-based buffer overflow in the xioscan_readline function in xio-readline.c in socat 1.4.0.0 through 1.7.2.0 and 2.0.0-b1 through 2.0.0-b4 allows l…EPSS 0.46%5.3CVE-2016-2217Dest-unreach socat vulnerabilityThe OpenSSL address implementation in Socat 1.7.3.0 and 2.0.0-b8 does not use a prime number for the DH, which makes it easier for remote attackers t…EPSS 2.5%2.6CVE-2013-3571Dest-unreach socat vulnerabilitysocat 1.2.0.0 before 1.7.2.2 and 2.0.0-b1 before 2.0.0-b6, when used for a listen type address and the fork option is enabled, allows remote attacker…EPSS 2.1%1.9CVE-2014-0019Dest-unreach socat memory buffer overflow vulnerabilityStack-based buffer overflow in socat 1.3.0.0 through 1.7.2.2 and 2.0.0-b1 through 2.0.0-b6 allows local users to cause a denial of service (segmentat…EPSS 0.40%9.3CVE-2026-94127F5 big-ip access policy manager heap-based buffer overflow vulnerabilityWhen a BIG-IP APM access policy and an OAuth profile are configured on a virtual server, specific malicious traffic can lead to remote code execution…KEVEPSS 2.2%9.8CVE-2025-25249Fortinet FortiOS and FortiSwitchManager heap buffer overflow via crafted packetsA heap-based buffer overflow (CWE-122/CWE-787) in Fortinet FortiOS 6.4 through 7.6.3 and FortiSwitchManager 7.0 through 7.2.6 lets an unauthenticated…KEVEPSS 3.9%analysed

Source: NIST National Vulnerability Database (record CVE-2026-56123), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.