{"id":"CVE-2026-33248","aliases":["BIT-nats-2026-33248","GHSA-3f24-pcvm-5jqc","GO-2026-4828"],"url":"https://o3.security/vulnerability/CVE-2026-33248","summary":"NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching","details":"### Background\n\nNATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.\n\nOne authentication model supported is mTLS, deriving the NATS client identity from properties of the TLS Client Certificate.\n\n### Problem Description\n\nWhen using mTLS for client identity, with `verify_and_map` to derive a NATS identity from the client certificate's Subject DN, certain patterns of RDN would not be correctly enforced, allowing for authentication bypass.\n\nThis does require a valid certificate from a CA already trusted for client certificates, and `DN` naming patterns which the NATS maintainers consider highly unlikely.\n\nSo this is an unlikely attack. Nonetheless, administrators who have been very sophisticated in their `DN` construction patterns might conceivably be impacted.\n\n### Affected Versions\n\nFixed in nats-server 2.12.6 & 2.11.15\n\n### Workarounds\n\nDevelopers should review their CA issuing practices.","published":"2026-03-25T20:18:28.923Z","modified":"2026-10-28T02:31:02.586841994Z","cvss":{"score":4.2,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N"},"epss":{"score":0.00143,"percentile":0.04005,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/nats-io/nats-server/v2","fixedVersion":"2.11.15"},{"ecosystem":"Go","name":"github.com/nats-io/nats-server/v2","fixedVersion":"2.12.6"},{"ecosystem":"Go","name":"github.com/nats-io/nats-server","fixedVersion":null}],"fix":null,"references":[{"type":"ADVISORY","url":"https://advisories.nats.io/CVE/secnote-2026-13.txt"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33248.json"},{"type":"ADVISORY","url":"https://github.com/nats-io/nats-server/security/advisories/GHSA-3f24-pcvm-5jqc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33248"},{"type":"PACKAGE","url":"https://github.com/nats-io/nats-server"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:02.586841994Z"}}