{"id":"CVE-2026-93599","aliases":["GHSA-82j2-j2ch-gfr8","RUSTSEC-2026-0104"],"url":"https://o3.security/vulnerability/CVE-2026-93599","summary":"rustls-webpki before 0.103.13 Panic via empty BIT STRING","details":"rustls-webpki through 0.103.12 (and 0.104.0-alpha releases before 0.104.0-alpha.7) contains a reachable panic in bit_string_flags() in src/der.rs. The input guard fails to reject a named-bit BIT STRING whose content is exactly [0x00] (zero padding bits and no data bytes), so raw_bits.len() - 1 underflows on the empty slice and the subsequent index operation panics (subtract-with-overflow in debug, index-out-of-bounds in release). The condition is reachable through the public API BorrowedCertRevocationList::from_der() when a CRL contains an issuingDistributionPoint extension with such an onlySomeReasons value. Exploitation requires an application that explicitly opts in to CRL revocation checking by passing RevocationOptions to verify_for_usage() and that parses CRL bytes obtained from a source the attacker can influence; the default rustls configuration, which does not use RevocationOptions, is unaffected. A crafted CRL causes a denial of service via the panic. Fixed in 0.103.13 and 0.104.0-alpha.7.","published":"2026-09-18T13:20:10.258Z","modified":"2026-09-20T11:30:34.342000320Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"crates.io","name":"rustls-webpki","fixedVersion":"0.103.13"},{"ecosystem":"crates.io","name":"rustls-webpki","fixedVersion":"0.104.0-alpha.7"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/93xxx/CVE-2026-93599.json"},{"type":"ADVISORY","url":"https://github.com/rustls/webpki/security/advisories/GHSA-82j2-j2ch-gfr8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-93599"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/rustls-webpki-before-0.103.13-panic-via-empty-bit-string"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-20T11:30:34.342000320Z"}}