CVE-2026-53583: Cert Validation Flaw (CVSS 6.5)

Description

libgit2 is a portable C implementation of the Git core methods provided as a linkable library with a solid API, allowing to build Git functionality into your application. Prior to 1.8.6 and 1.9.5, verify_server_cert in src/libgit2/streams/openssl.c uses an inverted !!memcmp result in the GEN_IPADD branch when comparing an IP-literal host with a certificate IP SubjectAltName. OpenSSL builds reject matching IP addresses and accept mismatched IP addresses, allowing a network attacker with a CA-trusted certificate containing any IP SubjectAltName to intercept libgit2 connections to IP-literal HTTPS URLs. DNS SubjectAltName validation and non-OpenSSL TLS backends are not affected. This issue is fixed in versions 1.8.6 and 1.9.5.

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CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0019

Probability of exploitation

0.09%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-295 CWE-295

CWE-297 CWE-297

References

Other References

https://github.com/libgit2/libgit2/commit/647dcb432980b84ede4cb5a008bbd1ccb4ead03d https://github.com/libgit2/libgit2/commit/c2aa35409ee0e6515df64da49750f13a0a42c47f https://github.com/libgit2/libgit2/commit/ef086bc3e4eedf62be38a910381aae24d49871ff https://github.com/libgit2/libgit2/releases/tag/v1.8.6 https://github.com/libgit2/libgit2/releases/tag/v1.9.5 https://github.com/libgit2/libgit2/security/advisories/GHSA-h7gc-w2gg-p9xp https://github.com/libgit2/libgit2/security/advisories/GHSA-h7gc-w2gg-p9xp

Frequently Asked Questions

What is CVE-2026-53583? +

libgit2 is a portable C implementation of the Git core methods provided as a linkable library with a solid API, allowing to build Git functionality into your application. Prior to 1.8.6 and 1.9.5, verify_server_cert in src/libgit2/streams/openssl.c uses an inverted !!memcmp result in the GEN_IPADD branch when comparing an IP-literal host with a certificate IP SubjectAltName. OpenSSL builds reject matching IP addresses and accept mismatched IP addresses, allowing a network attacker with a CA-trusted certificate containing any IP SubjectAltName to intercept libgit2 connections to IP-literal HTTPS URLs. DNS SubjectAltName validation and non-OpenSSL TLS backends are not affected. This issue is fixed in versions 1.8.6 and 1.9.5. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-53583? +

CVE-2026-53583 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0019, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-53583? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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