CVE-2026-27889

moderate-risk
Published 2026-03-25

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.

Do I need to act?

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0.08% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
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Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
7
CVSS 7.5/10 High
NETWORK / LOW complexity

Affected Products (1)

Affected Vendors

Linuxfoundation

References (2)

Mitigation https://advisories.nats.io/CVE/secnote-2026-03.txt
Mitigation https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6
31
/ 100
moderate-risk
Severity 26/34 · High
Exploitability 0/34 · Minimal
Exposure 5/34 · Minimal