CVE-2026-56123
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedsocat 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceHeap-based buffer overflow in socat SOCKS5 proxy domain name reply parser caused by sign-extension flaw. A signed char field reads the domain name length byte; when negative, implicit conversion to size_t yields a large unsigned value, resulting in unbounded heap write into 262-byte reply buffer with attacker-controlled size and content.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 1.8.0.0, < 1.8.1.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check if socat is installedRun 'which socat' or 'socat -V' to locate and verify the socat binary exists on the systemAffected if socat is not found on the system, then this CVE does not apply
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Identify the installed socat versionRun 'socat -V' and parse the version string from the output. Compare the version against the affected range: >= 1.8.0.0 and < 1.8.1.2Affected if The installed version falls within >= 1.8.0.0 and < 1.8.1.2, meaning the vulnerability is present in this binary
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Determine if SOCKS5 protocol support is in useReview any socat command lines, scripts, or configuration files for SOCKS5 connections (look for 'SOCKS5' or 'socks5' in the command arguments)Affected if SOCKS5 connections are actively used or configured with socat, making the DOMAINNAME reply parser reachable
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Check for untrusted SOCKS5 proxy connectionsInspect running socat processes and their arguments to identify the target SOCKS5 proxy server; verify whether the proxy is trusted or potentially untrustedAffected if socat is connecting through untrusted or unknown SOCKS5 proxy servers, which is the attack vector for this vulnerability
You are affected if socat version 1.8.0.0 through 1.8.1.1 is installed AND the SOCKS5 protocol feature is being used to connect through any SOCKS5 proxy server
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped1.8.1.2
Upgrade socat to version 1.8.1.2 or later; if upgrade not immediately possible, disable SOCKS5 proxy functionality or restrict network exposure to trusted proxy servers.
socat 1.8.1.2 or later
- 1. Identify the current socat version installed on the system (e.g., run 'socat -V' or 'socat --version')
- 2. Obtain socat version 1.8.1.2 or later from the official source at www.dest-unreach.org/socat/
- 3. Upgrade socat by installing the new version using your system's package manager or by compiling from source
- 4. Verify the upgrade was successful by checking the installed version matches or exceeds 1.8.1.2
- 5. Test that critical socat-based workflows function correctly after the upgrade
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 h
- Testing5.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-56123 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-56123 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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