CVE-2026-56123: socat 1.8.0.0 - 1.8.1.1 Heap Buffer Overflow via SOCKS5 Reply Parser
Vulnerability summary
CVE-2026-56123 is a critical (CVSS 9.8) Heap-based Buffer Overflow vulnerability in dest-unreach socat. EPSS estimates a 0.31% chance of exploitation in the next 30 days, higher than 24.4% of scored vulnerabilities.
Severe, CVSS 9.2 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 1 · Related 1Timeline
- 25-06-2026PublishedVulnerability first disclosed.
- 14-07-2026Last modifiedVulnerability information updated.
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 metrics
8 scores · 5 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated9.2CriticalCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- NVDNIST9.2CriticalCVSS: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
- CVE.orgCNA8.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HDiffers
- OSV · AlpineEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · UbuntuEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS trend
Probability
0.31%
Chance of exploitation in the next 30 days
Percentile
24%
Versus all other CVEs
30-day change
Decrease -0.23 pp
From 0.55% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Mageia2 products
- socat< 1.8.1.0-1.1.mga10
- socat< 1.8.0.2-1.1.mga9
Alpine1 product
- socat≥ 1.8.0.0, < 1.8.1.2-r0
Debian1 product
- socat< 1.8.0.3-1+deb13u1 | < 1.8.1.3-1
Dest-unreach1 product
- socat≥ 1.8.0.0, < 1.8.1.2
Opensuse1 product
- socat&distro=openSUSE Tumbleweed< 1.8.1.3-1.1
Socat1 product
- socat≥ 1.8.0.0, < 1.8.1.2
Ubuntu1 product
- socat< 1.8.0.0-4ubuntu0.1 | All versions (No fix recorded) | < 1.8.1.1-1ubuntu0.1
7 vendors · 8 products
References
11 links- www.vulncheck.com/advisories/socat-heap-buffer-overflow-via-socks5-reply-parserThird Party Advisory
