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. 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.
Vulnerability class: Buffer Overflow
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.005 (43.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 44th percentile — 43.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Dest-Unreach Socat
- Socat — versions 1.8.0.0
Weakness classification (CWE)
References
- www.dest-unreach.org/socat/CHANGES (release-notes, Release Notes, patch)
- www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parser (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.