libgit2 up to 1.8.5/1.9.4 OpenSSL TLS Backend openssl.c verify_server_cert certificate validation

Summaryinfo

A vulnerability was found in libgit2 up to 1.8.5/1.9.4. It has been classified as problematic. The affected element is the function verify_server_cert of the file src/libgit2/streams/openssl.c of the component OpenSSL TLS Backend. The manipulation leads to certificate validation. This vulnerability is traded as CVE-2026-53583. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in libgit2 up to 1.8.5/1.9.4. It has been rated as problematic. This issue affects the function verify_server_cert of the file src/libgit2/streams/openssl.c of the component OpenSSL TLS Backend. The manipulation with an unknown input leads to a certificate validation vulnerability. Using CWE to declare the problem leads to CWE-295. The product does not validate, or incorrectly validates, a certificate. Impacted is integrity. The summary by CVE is:

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 is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-53583 since 06/09/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1587.003 according to MITRE ATT&CK.

Upgrading to version 1.8.6 or 1.9.5 eliminates this vulnerability.

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Productinfo

Name

• libgit2

Version

• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5
• 1.9.0
• 1.9.1
• 1.9.2
• 1.9.3
• 1.9.4

Website

• Product: https://github.com/libgit2/libgit2/

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