CVE-2026-27571: GO-2026-4533 - nats-server websockets are vulnerable to pre-auth memory DoS in github.com/nats-io/nats-server

CVE-2026-27571 · Severity: low · CVSS 3.1 · Published 2026-02-25

nats-server websockets are vulnerable to pre-auth memory DoS in github.com/nats-io/nats-server

Technologies: github.com/nats-io/nats-server (Go), github.com/nats-io/nats-server/v2 (Go). Vendors: Go.

Quick answers

Is CVE-2026-27571 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-27571 being exploited in the wild.
How severe is CVE-2026-27571?
Low severity, with a CVSS score of 3.1, published 25 February 2026.
Which products and versions are affected?
github.com/nats-io/nats-server (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.4.1; github.com/nats-io/nats-server/v2 (Go) SEMVER:introduced=0,fixed=2.11.12, SEMVER:introduced=0,fixed=2.11.12,introduced=2.12.0-RC.1,fixed=2.12.3.
Is there a fix for CVE-2026-27571?
Yes. github.com/nats-io/nats-server/v2 (Go): upgrade to 2.11.12, 2.12.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-27571?
Check whether you run github.com/nats-io/nats-server (Go) or github.com/nats-io/nats-server/v2 (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • github.com/nats-io/nats-server/v2 (Go): upgrade to 2.11.12, 2.12.3 or later
    go get github.com/nats-io/nats-server/v2@v2.12.3

Affected products

  • github.com/nats-io/nats-server (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.4.1
  • github.com/nats-io/nats-server/v2 (Go) SEMVER:introduced=0,fixed=2.11.12, SEMVER:introduced=0,fixed=2.11.12,introduced=2.12.0-RC.1,fixed=2.12.3

Identifiers

  • CVE-2026-27571
  • GHSA-qrvq-68c2-7grw
  • GO-2026-4533

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