What’s Vulnerable › Vulnerabilities

CVE-2026-27889: NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-25 · updated 2026-09-09
• Weakness: CWE-190

Description

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 products

• nats-io nats-server: from 2.2.0 before 2.11.14; from 2.12.0 before 2.12.5 — fixed in 2.11.14, 2.12.5

How to fix

Upgrade to a fixed version: nats-io nats-server 2.11.14, 2.12.5. Check the vendor advisory for mitigations.

References

• https://advisories.nats.io/CVE/secnote-2026-03.txt
• https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6
• https://access.redhat.com/errata/RHSA-2026:21769
• https://access.redhat.com/errata/RHSA-2026:22347
• https://access.redhat.com/errata/RHSA-2026:23345
• 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

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