CVE-2026-56123: socat versions 1.8.0.0 through 1.8.1.1 contain a heap-based buffer overflow vulnerability that allows a malici

Routine

HIGH 8.1REMOTEUPGRADE

CVE-2026-56123 is a high-severity flaw (CVSS 8.1) affecting socat. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 76%)
CISA exploited list	No
Weakness	CWE-122
Published	2026-06-25
Last modified	2026-06-26

Publisher (CNA): VulnCheck · Vendor: dest-unreach

Last updated 2026-06-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-25 17:17 UTCPublished CVE record published
2026-06-26 16:50 UTCUpdated Record last modified

dest-unreach socat UPGRADE

Affected: >= 1.8.0.0 and < 1.8.1.2

Fixed in: 1.8.1.2

Safe to downgrade to: a release before 1.8.0.0

1. Check installed version

apt-cache policy socat || rpm -q socat || socat --version

2. UPGRADE to 1.8.1.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade socat

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade socat

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.8.0.0 (Debian / Ubuntu)

apt-cache madison socat sudo apt install socat=<VERSION_BEFORE_1.8.0.0> sudo apt-mark hold socat

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list socat sudo dnf downgrade socat-<VERSION_BEFORE_1.8.0.0> sudo dnf versionlock add socat

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-56123?

socat: upgrade to 1.8.1.2. Exact commands for each OS are on this page.

Is CVE-2026-56123 being exploited?

CVE-2026-56123 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-56123 affect?

CVE-2026-56123 affects socat. Severity is high (CVSS 8.1). 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. Duri

How urgent is CVE-2026-56123?

Priority 39/100. High severity; Remotely exploitable, no login, no user action

References

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