Home/CVE/NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.
CVE

CVE-2026-27889

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.

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.

HIGH · CVSS 7.5 EPSS 0.00094
Schedule remediation
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-190Integer Overflow or Wraparound
▤

Affected Products & Versions

2
linuxfoundation nats-server>= 2.2.0 and < 2.11.14
linuxfoundation nats-server>= 2.12.0 and < 2.12.5
▤

Affected Packages

2
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Go github.com/nats-io/nats-server HIGH
Go github.com/nats-io/nats-server/v2 HIGH fixed in 2.11.14
▣

Scoring & Timeline

7.5
HIGH · CVSS v3.1 · security-advisories@github.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD25 Mar 2026 · 08:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
SSVC triage · cisa-vulnrichment
Exploitation
poc
Automatable
yes
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

2
rhsaRHSA-2026:21769Important
rhsaRHSA-2026:22347Important
🔗

References & Sources

2
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://advisories.nats.io/CVE/secnote-2026-03.txtMitigationVendor Advisory
https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6MitigationVendor Advisory
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