CVE-2026-56123

Publication date 25 June 2026

Last updated 29 June 2026

Ubuntu priority

Cvss 3 Severity Score

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
socat	26.04 LTS resolute	Needs evaluation
	25.10 questing	Needs evaluation
	24.04 LTS noble	Needs evaluation
	22.04 LTS jammy	Needs evaluation
	20.04 LTS focal	Needs evaluation
	18.04 LTS bionic	Needs evaluation
	14.04 LTS trusty	Needs evaluation

Severity score breakdown

CVSS version:

Base score 9.2 · Critical

Base metrics

Parameter	Value
Attack vector	Network
Attack complexity	High
Attack requirements	None
Privileges required	None
User interaction	None
Vulnerable system - Confidentiality impact	High
Vulnerable system - Integrity impact	High
Vulnerable system - Availability impact	High
Subsequent system - Confidentiality impact	None
Subsequent system - Integrity impact	None
Subsequent system - Availability impact	None

Scores

Parameter	Value
Base score	9.2 · Critical
Base + Threat score	-
Base + Environmental score	-
Base + Threat + Environmental score	-

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

Base score 8.1 · High