Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-07-08T19:43:13 github.com/nats-io/nats-server: NATS Server: Authentication bypass and privilege escalation via parser fast path 8.8 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L CWE-551

NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.0, 2.12.7, and 2.11.16, when no_auth_user was configured, a parser fast path intended for ordinary client connections could also apply to route or leafnode listeners, allowing an unauthenticated peer to bypass inter-server CONNECT authentication and operate with the privileges associated with that connection type. This issue is fixed in versions 2.14.0, 2.12.7, and 2.11.16.

A flaw was found in NATS Server. When the `no_auth_user` configuration is enabled, a parser optimization intended for client connections can inadvertently apply to route or leafnode listeners. This allows an unauthenticated attacker on an adjacent network to bypass inter-server authentication. Consequently, the attacker can operate with the privileges of a trusted connection, leading to a high impact on data integrity.

This Important flaw in NATS Server permits an unauthenticated attacker on an adjacent network to bypass inter-server authentication when the `no_auth_user` configuration is active. This allows the attacker to operate with trusted connection privileges, leading to a high impact on data integrity. To mitigate this issue, avoid enabling the `no_auth_user` configuration in NATS Server. If `no_auth_user` is required, restrict network access to NATS route and leafnode listeners using firewall rules to only trusted hosts and networks. This limits the attack surface by preventing unauthenticated access from adjacent networks. A restart of the NATS server may be required for configuration changes to take effect. Red Hat Hardened Images Not affected nats-server2.12 Red Hat Hardened Images Not affected nats-server2.14 https://www.cve.org/CVERecord?id=CVE-2026-58253 https://nvd.nist.gov/vuln/detail/CVE-2026-58253 https://github.com/nats-io/nats-server/commit/7b81dd455ea95960090a84858c7662827948d1b6 https://github.com/nats-io/nats-server/commit/8b8e1ad4ceed32321e00d4fc6e76be05bc13bca6 https://github.com/nats-io/nats-server/commit/b86147e81710a52b72a7f7275f91d69f723f5cb3 https://github.com/nats-io/nats-server/releases/tag/v2.11.16 https://github.com/nats-io/nats-server/releases/tag/v2.12.7 https://github.com/nats-io/nats-server/releases/tag/v2.14.0 https://github.com/nats-io/nats-server/security/advisories/GHSA-38x3-76xf-cq45