Skip to content
Fencer Vulns
high 7.5

CVE-2026-27889 json

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

published 2026-03-25 7 mo ago modified 2026-09-10 1 mo ago also BIT-nats-2026-27889 , EUVD-2026-15962 , GHSA-pq2q-rcw4-3hr6 , GO-2026-4841 , JLSEC-2026-1121

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/nats-io/nats-server/v2 2.11.14, 2.12.5
  • bitnami nats 2.11.14, 2.12.5
  • julia nats_server_jll 2.14.3+0
  • Red Hat Multicluster Global Hub 1.4.5 1779579439
  • Red Hat Multicluster Global Hub 1.6.5 1780167118
  • Red Hat Red Hat multicluster global hub 1.5.3 1778867753
  • nats-server Debian 14 2.12.6-1

debian advisories DEBIAN-CVE-2026-27889

  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20260326T203309-150000.1.155.2

suse advisories SUSE-SU-2026:1135-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-27889 updated cvss 7.5

github.com/nats-io/nats-server: NATS-Server: Denial of Service via malformed WebSockets frame

  • Red Hat Multicluster Global Hub 1.4.9 multicluster-globalhub/multicluster-globalhub-grafana-rhel9 1779579439
    fixed: vendor fix RHSA-2026:22347
  • Red Hat Multicluster Global Hub 1.6.5 multicluster-globalhub/multicluster-globalhub-grafana-rhel9 1780167118
    fixed: vendor fix RHSA-2026:23345
  • Red Hat multicluster global hub 1.5.3 multicluster-globalhub/multicluster-globalhub-grafana-rhel9 1778867753
    fixed: vendor fix RHSA-2026:21769
  • Red Hat Multicluster Global Hub 1.4.9 multicluster-globalhub/multicluster-globalhub-agent-rhel9 1779838819, multicluster-globalhub/multicluster-globalhub-manager-rhel9 1779839447, multicluster-globalhub/multicluster-globalhub-rhel9-operator 1779887217, multicluster-globalhub/multicluster-globalhub-operator-bundle 1779891163, multicluster-globalhub/multicluster-globalhub-postgres-exporter-rhel9 1779147132 Red Hat Multicluster Global Hub 1.6.5 multicluster-globalhub/multicluster-globalhub-agent-rhel9 1780320809, multicluster-globalhub/multicluster-globalhub-manager-rhel9 1780321673, multicluster-globalhub/multicluster-globalhub-rhel9-operator 1779839087, multicluster-globalhub/multicluster-globalhub-operator-bundle 1780370487, multicluster-globalhub/multicluster-globalhub-postgres-exporter-rhel9 1779839762 Red Hat multicluster global hub 1.5.3 multicluster-globalhub/multicluster-globalhub-agent-rhel9 1779828691, multicluster-globalhub/multicluster-globalhub-manager-rhel9 1779828813, multicluster-globalhub/multicluster-globalhub-rhel9-operator 1779828536, multicluster-globalhub/multicluster-globalhub-operator-bundle 1779837290, multicluster-globalhub/multicluster-globalhub-postgres-exporter-rhel9 1779835152 Red Hat OpenShift Container Platform 4 openshift4/oc-mirror-plugin-rhel9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.59% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
go github.com/nats-io/nats-server/v2
>=2.2.0, <2.11.14
>=2.12.0, <2.12.5
2.11.14
2.12.5
go github.com/nats-io/nats-server
all versions
 no fix listed
bitnami nats
>=2.2.0, <2.11.14
>=2.12.0, <2.12.5
2.11.14
2.12.5
julia nats_server_jll
<2.14.3+0
2.14.3+0

Affected products

  • nats-io nats-server
  • Red Hat Multicluster Global Hub 1.4.5
  • Red Hat Multicluster Global Hub 1.6.5
  • Red Hat Red Hat multicluster global hub 1.5.3
  • Red Hat Red Hat OpenShift Container Platform 4

Classification

Weakness
  • CWE-190 Integer Overflow or Wraparound
  • CWE-1286 Improper Validation of Syntactic Correctness of Input

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.