CVE-2026-53583Public exploitNetwork attack vector

MITM interception via inverted IP SAN comparison

Published Aug 20, 2026 · Updated Aug 20, 2026

Certificate validation bypass in libgit2 before 1.8.6 and 1.9.5 allows network attackers to intercept HTTPS Git traffic via IP-literal URLs. In OpenSSL builds, verify_server_cert in src/libgit2/streams/openssl.c applies !!memcmp to GEN_IPADD SubjectAltName data, reversing host-IP matching so mismatched IP SANs are accepted and correct ones are rejected. Exploitation requires a man-in-the-middle position, an IP-literal HTTPS remote, and a CA-trusted certificate containing any IP SubjectAltName; DNS-name validation and non-OpenSSL backends are unaffected.

CVSS severity6.5
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Certificate validation bypass in libgit2 before 1.8.6 and 1.9.5 allows network attackers to intercept HTTPS Git traffic via IP-literal URLs. In OpenSSL builds, verify_server_cert in src/libgit2/streams/openssl.c applies !!memcmp to GEN_IPADD SubjectAltName data, reversing host-IP matching so mismatched IP SANs are accepted and correct ones are rejected. Exploitation requires a man-in-the-middle position, an IP-literal HTTPS remote, and a CA-trusted certificate containing any IP SubjectAltName; DNS-name validation and non-OpenSSL backends are unaffected.

The record

CVE
CVE-2026-53583
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
libgit2
Product
libgit2
Classifications
CWE-297, CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.8.6
  2. Affected versionversion=>= 1.9.0, < 1.9.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

libgit2 · libgit2version=< 1.8.6; version=>= 1.9.0, < 1.9.5

Published CVSS scores

6.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-297Improper Validation of Certificate with Host Mismatch
CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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