Subject: nats-server: Pre-auth panic and server hang via malformed JWT issuer (missing Ed25519 length check in nkeys)

NATS-advisory-ID: 2026-23
Aliases: GHSA-g33f-6538-grxh
Date: 2026-06-29
Fixed-In: v2.14.2, v2.12.10.


Background:

NATS.io is a high performance open source pub-sub distributed communication
technology, built for the cloud, on-premise, IoT, and edge computing.

The NATS Server can run in operator mode, deriving client identities and
permissions from JWT credentials signed with NKeys.


Problem Description:

An unauthenticated client could cause an operator-mode NATS Server to
panic while processing a client JWT before authentication completed.

The issue involved accepting a truncated public account key, which could
later reach Ed25519 signature verification with an invalid length. The
malformed key was taken from JWT claims processed during authentication
before a client identity had been established.


Affected Versions:

Versions v2.14.1, v2.12.9 and below are vulnerable.
The issue is fixed in v2.14.2 and v2.12.10.


Workarounds:

No known workaround for operator-mode deployments using JWT authentication. Upgrade to a fixed release.

Deployments not using operator-mode JWT authentication are not affected by this issue.


Credit:

GitHub user @queencitycyber


References:

 * This document is canonically:
   <https://advisories.nats.io/CVE/secnote-2026-23.txt>
 * GHSA advisory:
   <https://github.com/nats-io/nats-server/security/advisories/GHSA-g33f-6538-grxh>