CVE-2026-27889

Summary

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.

Affected Software

Weaknesses

• CWE-190: CWE-190: Integer Overflow or Wraparound

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

github.com/nats-io/nats-server: NATS-Server: Denial of Service via malformed WebSockets frame

Additional References

• https://access.redhat.com/security/cve/CVE-2026-27889
• https://bugzilla.redhat.com/show_bug.cgi?id=2451447
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27889.json
• https://access.redhat.com/errata/RHSA-2026:22347
• https://access.redhat.com/errata/RHSA-2026:21769
• https://access.redhat.com/errata/RHSA-2026:23345

References

• https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6
• https://advisories.nats.io/CVE/secnote-2026-03.txt

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