Vulnerability · Published Mar 25, 2026 · Assigned by GitHub_M
CVE-2026-27889NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead
High 7.5
In plain English
A high-severity integer overflow in nats-server from nats-io. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | nats-server | no fix listed | DEBIAN-CVE-2026-27889 |
| Debian:13 | nats-server | no fix listed | DEBIAN-CVE-2026-27889 |
| Debian:14 | nats-server | 2.12.6-1 | DEBIAN-CVE-2026-27889 |
| Go | github.com/nats-io/nats-server | no fix listed | GO-2026-4841 |
| Go | github.com/nats-io/nats-server | no fix listed | GHSA-pq2q-rcw4-3hr6 |
| Go | github.com/nats-io/nats-server/v2 | 2.11.14 | GHSA-pq2q-rcw4-3hr6 |
| Go | github.com/nats-io/nats-server/v2 | 2.12.5 | GHSA-pq2q-rcw4-3hr6 |
| Go | github.com/nats-io/nats-server/v2 | 2.11.14, 2.12.5 | GO-2026-4841 |
| Ubuntu:24.04:LTS | nats-server | no fix listed | UBUNTU-CVE-2026-27889 |
| Ubuntu:25.10 | nats-server | no fix listed | UBUNTU-CVE-2026-27889 |
| Ubuntu:26.10 | nats-server | no fix listed | UBUNTU-CVE-2026-27889 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| nats-io | nats-server | >= 2.2.0, < 2.11.14>= 2.12.0, < 2.12.5 |
Weakness: CWE-190, CWE-1286 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6 x_refsource_CONFIRM
- https://advisories.nats.io/CVE/secnote-2026-03.txt x_refsource_MISC
- https://access.redhat.com/security/cve/CVE-2026-27889 vdb-entry, x_refsource_REDHAT
- RHBZ#2451447 issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27889.json x_sadp-csaf-vex
- https://access.redhat.com/errata/RHSA-2026:22347 vendor-advisory, x_refsource_REDHAT
- https://access.redhat.com/errata/RHSA-2026:23345 vendor-advisory, x_refsource_REDHAT
- https://access.redhat.com/errata/RHSA-2026:21769 vendor-advisory, x_refsource_REDHAT