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Advisory record · GHSA-qrvq-68c2-7grw

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

CVSS 5.9 MediumEPSS 0.0054 · 45th percentile

Published by the GitHub Advisory Database at 24 Feb 2026, 16:04 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
github.com/nats-io/nats-server/v2Go<2.11.12 || >=2.12.0-RC.1, <2.12.32.11.12, 2.12.3
github.com/nats-io/nats-serverGo<=1.4.1No fixed version yet
Identifiers
GHSA-qrvq-68c2-7grw · BIT-nats-2026-27571 · CVE-2026-27571 · GO-2026-4533
Weakness (CWE)
CWE-409 · CWE-770
Tags
Published
24 Feb 2026
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The nats-server WebSocket handling is vulnerable to a pre-authentication memory exhaustion attack in the Go packages github.com/nats-io/nats-server/v2 before 2.11.12 and from 2.12.0-RC.1 before 2.12.3. An unauthenticated attacker who can reach the WebSocket port can send a compressed message that expands to excessive memory, which can crash the server process. Upgrade to version 2.11.12 or 2.12.3. Deployments that do not use WebSockets or expose the port to untrusted clients are not affected.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
5.9 Medium 3.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0054, the 45th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:13 UTC First seen by agentprime
  2. 31 Oct 2026, 14:13 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.