{"id":"UBUNTU-CVE-2026-93599","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.","modified":"2026-09-23T23:40:09Z","published":"2026-09-18T14:19:00Z","upstream":["CVE-2026-93599"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-93599"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-93599"},{"type":"REPORT","url":"https://github.com/rustls/webpki/security/advisories/GHSA-82j2-j2ch-gfr8"},{"type":"REPORT","url":"https://rustsec.org/advisories/RUSTSEC-2026-0104.html"},{"type":"REPORT","url":"https://www.vulncheck.com/advisories/rustls-webpki-before-0.103.13-panic-via-empty-bit-string"}],"affected":[{"package":{"name":"rust-rustls-webpki","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/rust-rustls-webpki?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.101.4-4","0.101.7-2.1"],"ecosystem_specific":{"binaries":[{"binary_name":"librust-rustls-webpki-dev","binary_version":"0.101.7-2.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-93599.json"}},{"package":{"name":"rust-rustls-webpki","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/rust-rustls-webpki?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.102.8-5","0.103.7-1","0.103.7-1build1","0.103.9+ds-1","0.103.9+ds-2"],"ecosystem_specific":{"binaries":[{"binary_version":"0.103.9+ds-2","binary_name":"librust-rustls-webpki-dev"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-93599.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"},{"type":"Ubuntu","score":"medium"}]}