CVE-2026-93602 in rustls-webpki
Summary
by MITRE • 09/18/2026
rustls-webpki versions before 0.103.10 and 0.104.0-alpha.5 contain faulty CRL authority-matching logic that compares only the first distributionPoint against each CRL's IssuingDistributionPoint, ignoring additional distributionPoints. Attackers with a compromised trusted issuing authority can present revoked certificates that pass revocation checks under UnknownStatusPolicy::Allow, or cause incorrect errors under the default deny policy.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in rustls-webpki versions prior to 0.103.10 and 0.104.0-alpha.5 stems from a critical flaw in the implementation of Certificate Revocation List authority-matching logic. This cryptographic library, which serves as a core component for TLS connections in Rust-based applications, failed to correctly validate the relationship between certificate revocation lists and their issuing authorities when multiple distribution points were present. Specifically, the code compared only the first entry within the CRL's IssuingDistributionPoint field against each available distribution point listed in the revoked certificate. This incomplete comparison logic ignored any subsequent or additional distribution points that might be specified by the Certificate Authority. In X.509 infrastructure, a single revocation list can contain multiple URLs for downloading updates or alternative sources of truth regarding certificate status. By restricting validation to only the first entry, the library created a scenario where valid revocation data located in secondary distribution points was effectively disregarded during the verification process.
This technical flaw has significant operational implications for systems relying on strict certificate validation policies. Under an UnknownStatusPolicy set to Allow, which permits connections even if revocation status cannot be definitively determined, attackers possessing credentials from a compromised trusted issuing authority could present certificates that had been revoked but were not correctly flagged as such due to the faulty matching logic. Consequently, these invalid certificates would pass verification checks, allowing unauthorized access or man-in-the-middle attacks against secure communications. Conversely, under the default deny policy, which typically blocks connections when revocation status is unknown or negative, an attacker could potentially cause incorrect error states by exploiting mismatches between the limited set of distribution points checked and those actually containing valid revocation data. This inconsistency undermines the reliability of trust decisions made by applications using this library, leading to either false positives in security blocking or false negatives in authentication verification.
From a standards perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the software failed to properly validate all relevant inputs required for correct revocation checking. It also relates to CWE-697 Incorrect Comparison, specifically regarding the failure to iterate through and evaluate all available distribution points in the CRL structure. In terms of threat modeling, this flaw facilitates attacks categorized under MITRE ATT&CK technique T1078 Valid Accounts, as it allows compromised credentials to remain valid despite revocation notices. The issue highlights a common pitfall in cryptographic library development where edge cases involving complex X.509 structures are not exhaustively tested against all possible configurations defined by RFC 5280 and related standards for Online Certificate Status Protocol and CRL distribution points.
To mitigate this vulnerability, organizations utilizing rustls-webpki must immediately upgrade to version 0.103.10 or later, which includes the corrected authority-matching logic that properly iterates through all specified distribution points in a CRL's IssuingDistributionPoint field. Developers should verify their dependency trees to ensure no older versions are being pulled transitively by other libraries. Additionally, security teams should review application logs for any anomalies related to certificate validation failures or unexpected connection successes from previously revoked authorities. Implementing defense-in-depth strategies such as strict OCSP stapling where supported can further reduce reliance on CRL distribution point resolution alone, although the underlying library flaw must still be addressed at its source to ensure comprehensive protection against sophisticated revocation bypass attacks.