What is CVE-2026-56123?

CVE-2026-56123 is a high-severity vulnerability in Dest-unreach Socat, classified under Heap-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-06-25.

How severe is CVE-2026-56123?

High severity. CVSS v3 base score is 8.1 out of 10.

Buffer overflow in Dest-unreach Socat

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. Dur…

Vulnerability class: Buffer Overflow

EPSS: 0.003 (23.1th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Dest-unreach Socat
Socat — versions 1.8.0.0

Weakness classification (CWE)

CWE-122 — Heap-based Buffer Overflow

References

disclosure@vulncheck.com (release-notes, Release Notes, patch)
disclosure@vulncheck.com (Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2026-56123?: CVE-2026-56123 is a high-severity vulnerability in Dest-unreach Socat, classified under Heap-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-06-25.
How severe is CVE-2026-56123?: High severity. CVSS v3 base score is 8.1 out of 10.