Authentication bypass and privilege escalation via parser fast path

Summary

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. Red Hat severity: Important — CVSS 8.8 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L). Weakness: CWE-551. No fixing RHSA erratum has published yet; monitor the Red Hat CVE page and patch when it ships.