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VulnerabilityPublished

CVE-2026-33248: nats-server · Improper Authentication

Affects nats-serverSource CVE Database V5

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Not known to be exploited · CVSS 4.2 Medium : upgrade to 2.12.6 or 2.11.15 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
4.2Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 4% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.12.6, 2.11.15
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 25 Mar 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade nats-server to 2.12.6 or 2.11.15; nats-io/nats-server to 2.11.15.

Affected software

ProductAffectedFixed in
nats-ionats-serverAffected
  • >=2.12.0-RC.1 <2.12.6
Fixed in
  • 2.12.6
nats-ionats-serverAffected
  • <2.11.15
Fixed in
  • 2.11.15
GitHubnats-io/nats-serverpkg:github/nats-io/nats-serverOther threatsAffected
  • <2.11.15
Fixed in
  • 2.11.15

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-33248, organizations should upgrade nats-server to versions 2.11.15 or 2.12.6 or later, where the vulnerability is fixed. In the interim, administrators should audit and tighten their CA certificate issuance policies to prevent issuance of certificates with DN patterns that could be exploited. Review and restrict the use of the 'verify_and_map' feature if possible, or implement additional validation layers on client certificates. Employ strict monitoring and logging of client authentication attempts to detect anomalous DN patterns or unexpected client identities. Consider using alternative authentication mechanisms or multi-factor authentication to reduce reliance on DN pattern mapping. Regularly review and update TLS configurations and certificate trust stores to minimize risks from compromised or misissued certificates. Finally, maintain awareness of any emerging exploit reports and apply patches promptly.

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.

References

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