How severe is CVE-2026-56123?

CVE-2026-56123 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-56123 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-56123?

CVE-2026-56123 affects Dest-unreach Socat. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-56123?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-56123 have an EU (EUVD) identifier?

Yes. CVE-2026-56123 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39455.

When was CVE-2026-56123 published?

CVE-2026-56123 was published on 2026-06-25 and last updated on 2026-06-26.

CVE-2026-56123

CVE-2026-56123 is a high-severity vulnerability in Dest-unreach Socat with a CVSS 3.x base score of 8.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-122.

Key facts

Severity: High (CVSS 3.x base score 8.1)
CVSS v4: 9.2
EPSS exploit prediction: 0% (23rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-39455
Weakness: CWE-122
Affected product: Dest-unreach Socat
Published: 2026-06-25
Last modified: 2026-06-26

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-56123?: CVE-2026-56123 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-56123 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-56123?: CVE-2026-56123 affects Dest-unreach Socat. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-56123?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-56123 have an EU (EUVD) identifier?: Yes. CVE-2026-56123 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39455.
When was CVE-2026-56123 published?: CVE-2026-56123 was published on 2026-06-25 and last updated on 2026-06-26.

References

Affected products (1)

cpe:2.3:a:dest-unreach:socat:*:*:*:*:*:*:*:*

More vulnerabilities in Dest-unreach Socat

CVE-2015-1379 — High (CVSS 7.5): The signal handler implementations in socat before 1.7.3.0 and 2.0.0-b8 allow remote attackers to cause a denial of…
CVE-2010-2799 — Medium (CVSS 6.8): Stack-based buffer overflow in the nestlex function in nestlex.c in Socat 1.5.0.0 through 1.7.1.2 and 2.0.0-b1 through…
CVE-2012-0219 — Medium (CVSS 6.2): Heap-based buffer overflow in the xioscan_readline function in xio-readline.c in socat 1.4.0.0 through 1.7.2.0 and…
CVE-2016-2217 — Medium (CVSS 5.3): The OpenSSL address implementation in Socat 1.7.3.0 and 2.0.0-b8 does not use a prime number for the DH, which makes it…
CVE-2013-3571 — Low (CVSS 2.6): socat 1.2.0.0 before 1.7.2.2 and 2.0.0-b1 before 2.0.0-b6, when used for a listen type address and the fork option is…
CVE-2014-0019 — Low (CVSS 1.9): Stack-based buffer overflow in socat 1.3.0.0 through 1.7.2.2 and 2.0.0-b1 through 2.0.0-b6 allows local users to cause…

All CVEs affecting Dest-unreach Socat →

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