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TI-2026-21964 Aliases CVE-2026-27571GHSA-qrvq-68c2-7grw

nats-server websockets are vulnerable to pre-auth memory DoS

Priority LOW 34CWE-409Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Partial Red Hat: 2 fixed, 3 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-770.

Summary

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. The WebSockets handling of NATS messages handles compressed messages via the WebSockets negotiated compression. Prior to versions 2.11.2 and 2.12.3, the implementation bound the memory size of a NATS message but did not independently bound the memory consumption of the memory stream when constructing a NATS message which might then fail validation for size reasons. An attacker can use a compression bomb to cause excessive memory consumption, often resulting in the operating system terminating the server process. The use of compression is negotiated before authentication, so this does not require valid NATS credentials to exploit. The fix, present in versions 2.11.2 and 2.12.3, was to bounds the decompression to fail once the message was too large, instead of continuing on. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00542 45th percentileScored 2026-11-07
Fix Partial nats-server (nats-io): 2.11.12, 2.12.3github.com/nats-io/nats-server/v2 (Go): 2.11.12, 2.12.3Red Hat: 2 advisoriesRed Hat: 2 fixed, 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
backstagenats-serverbefore 2.11.12; 2.12.0-RC.1 to before 2.12.32.11.12, 2.12.3Patch availableCNA
—github.com/nats-io/nats-server/v2 (Go)before 2.11.122.11.12Patch availableGHSA-qrvq-68c2-7grw
—github.com/nats-io/nats-server/v2 (Go)2.12.0-RC.1 to before 2.12.32.12.3Patch availableGHSA-qrvq-68c2-7grw
—github.com/nats-io/nats-server (Go)up to 1.4.1—No fix listedGHSA-qrvq-68c2-7grw
  • nats-server Vendorbackstage Affected before 2.11.12; 2.12.0-RC.1 to before 2.12.3 Fixed in 2.11.12, 2.12.3 Patch available CNA
  • github.com/nats-io/nats-server/v2 (Go) Vendor— Affected before 2.11.12 Fixed in 2.11.12 Patch available GHSA-qrvq-68c2-7grw
  • github.com/nats-io/nats-server/v2 (Go) Vendor— Affected 2.12.0-RC.1 to before 2.12.3 Fixed in 2.12.3 Patch available GHSA-qrvq-68c2-7grw
  • github.com/nats-io/nats-server (Go) Vendor— Affected up to 1.4.1 Fixed in — No fix listed GHSA-qrvq-68c2-7grw

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*before 2.11.12; 2.12.0 to before 2.12.3Vulnerablebackstage
  • cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:* Versions before 2.11.12; 2.12.0 to before 2.12.3 Vulnerable ·backstage

Remediation

  • Fix · CNA nats-server (nats-io) Fixed in 2.11.12, 2.12.3
  • Fix · GHSA-qrvq-68c2-7grw github.com/nats-io/nats-server/v2 (Go) Fixed in 2.11.12 Advisory →
  • Fix · GHSA-qrvq-68c2-7grw github.com/nats-io/nats-server/v2 (Go) Fixed in 2.12.3 Advisory →

Red Hat 2 advisories

  • RHSA-2026:6226 Released 2026-03-31 · Red Hat rating Important
    Multicluster Global Hub 1.6.2 security update
    • Multicluster Global Hub 1.6.6 registry.redhat.io/multicluster-globalhub/multicluster-globalhub-agent-rhel9, registry.redhat.io/multicluster-globalhub/multicluster-globalhub-grafana-rhel9, registry.redhat.io/multicluster-globalhub/multicluster-globalhub-manager-rhel9 +2
  • RHSA-2026:5110 Released 2026-03-19 · Red Hat rating Important
    Multicluster Global Hub 1.5.4 security update
    • Multicluster Global Hub 1.5.8 registry.redhat.io/multicluster-globalhub/multicluster-globalhub-agent-rhel9, registry.redhat.io/multicluster-globalhub/multicluster-globalhub-grafana-rhel9, registry.redhat.io/multicluster-globalhub/multicluster-globalhub-manager-rhel9 +2

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Advanced Cluster Management for Kubernetes 2AffectedNo fix yet
Red Hat Ceph Storage 7AffectedNo fix yet: Fix deferred
Red Hat Ceph Storage 8AffectedNo fix yet: Fix deferred
Multicluster Global Hub 1.6.5Fixed RHSA-2026:6226
Red Hat multicluster global hub 1.5.3Fixed RHSA-2026:5110
Not affected: 3 products
  • Multicluster Global Hub 1.6.5
  • Red Hat OpenShift Container Platform 4
  • Red Hat multicluster global hub 1.5.3

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-27571
  2. 2026-10-03 Alias added: GHSA-qrvq-68c2-7grw
  3. 2026-10-25 EPSS moved to the below the 50th percentile

References

Patch 1

Advisory 2

Other 4

  • TI-2026-22233 NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead CVSS 3.1HIGH 7.5
  • TI-2022-11116 NATS nats-server 2.2.0 through 2.7.4 allows directory traversal because of an unintended… CVSS 3.1CRITICAL 9.8
  • TI-2020-16319 The JWT library in NATS nats-server before 2.1.9 has Incorrect Access Control because of… CVSS 3.1CRITICAL 9.8
  • TI-2026-25637 NATS has MQTT plaintext password disclosure CVSS 3.1HIGH 8.6
  • TI-2022-08320 NATS nats-server before 2.7.2 has Incorrect Access Control. CVSS 3.1HIGH 8.8
  • TI-2026-41950 NATS Server: Pre-auth server crash via double INFO in leafnode handshake CVSS 3.1HIGH 7.5
See all 35 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences