Incorrect authorization in nats-server - #VU135931
Published: June 30, 2026
Vulnerability identifier: #VU135931
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: N/A
CWE-ID: CWE-863
Exploitation vector: Remote access
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 user to gain unauthorized access to permissions assigned to the default user.
The vulnerability exists due to improper access control in the pre-CONNECT fast path when processing a first client operation other than CONNECT. A remote user can send an initial non-CONNECT operation to gain unauthorized access to permissions assigned to the default user.
Only deployments that use no_auth_user together with restrictions such as allowed_connection_types or proxy_required are vulnerable.
Remediation
Install security update from vendor's website.