{"id":"CVE-2026-33248","aliases":["GHSA-3f24-pcvm-5jqc","BIT-nats-2026-33248","GO-2026-4828"],"title":"NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching","summary":"NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching","severity":"medium","cvss":4.2,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N","vendor":"nats-io","product":"github.com/nats-io/nats-server/v2","ecosystem":"go","affected":["github.com/nats-io/nats-server/v2 < 2.11.15","github.com/nats-io/nats-server/v2 >= 2.12.0-RC.1, < 2.12.6","github.com/nats-io/nats-server"],"patched":["github.com/nats-io/nats-server/v2 2.11.15","github.com/nats-io/nats-server/v2 2.12.6"],"published":"2026-03-24","updated":"2026-09-10","sourceUpdated":"2026-09-10T03:50:36.808606306Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-3f24-pcvm-5jqc","references":[{"url":"https://github.com/nats-io/nats-server/security/advisories/GHSA-3f24-pcvm-5jqc"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33248"},{"url":"https://advisories.nats.io/CVE/secnote-2026-13.txt"},{"url":"https://github.com/nats-io/nats-server"}],"tags":["osv","go"],"epss":0.00143,"epssPercentile":0.04007,"ingestedAt":"2026-09-12T03:13:01.748Z","slug":"CVE-2026-33248","body":"## Overview\n\n### 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.\n\n## Affected packages\n\n- `github.com/nats-io/nats-server/v2 < 2.11.15`\n- `github.com/nats-io/nats-server/v2 >= 2.12.0-RC.1, < 2.12.6`\n- `github.com/nats-io/nats-server`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/nats-io/nats-server/v2 2.11.15`\n- `github.com/nats-io/nats-server/v2 2.12.6`","depth":"sunlit","depthScore":23,"depthScoreParts":{"impact":23.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}