CVE-2026-33248
NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching
- State
- Published
- Severity
- 4.2 Medium
- Published
- Mar 25, 2026
- Updated
- Mar 26, 2026
- Reserved
- Mar 18, 2026
Description
NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, when 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. This does require a valid certificate from a CA already trusted for client certificates, and `DN` naming patterns which the NATS maintainers consider highly unlikely. So this is an unlikely attack. Nonetheless, administrators who have been very sophisticated in their `DN` construction patterns might conceivably be impacted. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, developers should review their CA issuing practices.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 4.2 Medium | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N | GitHub_M |
Weaknesses
Affected Products
| Product | Versions |
|---|---|
nats-servernats-io |
|
References
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