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.
CSIRTS triage
- What
- The OpenSSL backend in libgit2 performs inverted IP SubjectAltName comparison during TLS certificate validation, allowing authentication bypass.
- Who is affected
- Systems using libgit2 with OpenSSL for TLS connections to remote Git repositories.
- Urgency
- Medium severity (CVSS 6.5) and not yet exploited; deploy patches in the next update cycle.
- Action
- Upgrade libgit2 to a version with corrected certificate validation logic for IP addresses in SubjectAltName fields.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.24% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 15% of all EPSS-scored CVEs.
Advisory coverage (3)
- mediumCVE-2026-53583: libgit2 is a portable C implementation of the Git core methods provided as a linkable library …nvd · 2026-08-20
- lowDSA-6453-1 libgit2 - security updatedebian · 2026-08-20
- mediumCVE-2026-53583: libgit2: Inverted IP SubjectAltName Comparison in OpenSSL Backendmsrc · 2026-08-11
External references
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