Auth bypass in Linuxfoundation Nats-Server
CVE-2026-33248
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.
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.2 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (5.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 6th percentile — 5.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.000
Affected products
- Linuxfoundation Nats-Server
- Nats-Io Nats-Server — versions < 2.11.15, >= 2.12.0-RC.1, < 2.12.6
Weakness classification (CWE)
References
- github.com/nats-io/nats-server/security/advisories/GHSA-3f24-pcvm-5jqc (Vendor Advisory)
- advisories.nats.io/CVE/secnote-2026-13.txt (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-33248?
- CVE-2026-33248 is a medium-severity vulnerability in Linuxfoundation Nats-Server, classified under Improper Authentication. CVSS score: 4.2/10. Published 2026-03-25.
- How severe is CVE-2026-33248?
- Medium severity. CVSS v3 base score is 4.2 out of 10.