High severity · published Mar 25, 2026
CVE-2026-27889
NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead
7.5
CVSS
0.6%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 48% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NA
nats-server · nats-io
>= 2.2.0, < 2.11.14; >= 2.12.0, < 2.12.5 · source: vendor, NVD
MG
Multicluster Global Hub 1.4.5 · Red Hat
All versions, or not specified · source: CISA
MG
Multicluster Global Hub 1.6.5 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat multicluster global hub 1.5.3 · Red Hat
All versions, or not specified · source: CISA
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27889
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27889
Mitigation
https://advisories.nats.io/CVE/secnote-2026-03.txt
Mitigation
https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:21769
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:22347
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:23345
access.redhat.com
https://access.redhat.com/security/cve/CVE-2026-27889
More from nats-server
8.8
CVE-2026-58253
NATS Server: Route API Auth Bypass
7.5
CVE-2026-58208
NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is Enabled
7.5
CVE-2026-58210
NATS Server: MQTT partial CONNECT packets can exhaust pre-auth memory
7.5
CVE-2026-58250
NATS Server: Pre-auth server crash via double INFO in leafnode handshake
7.5
CVE-2026-33218
NATS has pre-auth server panic via leafnode handling