Improper Authentication in nats-server - #VU135926
Published: June 30, 2026
Vulnerability identifier: #VU135926
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: N/A
CWE-ID: CWE-287
Exploitation vector: Adjecent network
Exploit availability:
No public exploit available
Vendor: NATS - The Cloud Native Messaging System
Affected software:
nats-server
nats-server
Detailed vulnerability description
The vulnerability allows a remote attacker to bypass authentication and gain privileges associated with inter-server connection types.
The vulnerability exists due to improper authentication in route or leafnode listeners when processing connections before the inter-server CONNECT authentication flow completes. A remote attacker can connect to an affected listener and exploit the parser fast path to bypass authentication and gain privileges associated with inter-server connection types.
The issue occurs when no_auth_user is configured.
Remediation
Install security update from vendor's website.