CVE-2026-33248 Linuxfoundation — Exploit & Vulnerability Details MEDIUM

Parameter	Value
CVSS	4.2 (MEDIUM)
Affected Versions	2.12.0 — 2.12.6
Fixed In	2.11.15
Type	CWE-295 (Improper Certificate Validation), CWE-287 (Improper Authentication)
Vendor	Linuxfoundation
Public PoC	No

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, when using mTLS for client identity, with `verify_and_map` to derive a NATS identity from the client certificate's Subject DN, certain patterns of RDN would not be correctly enforced, allowing for authentication bypass. This does require a valid certificate from a CA already trusted for client certificates, and `DN` naming patterns which the NATS maintainers consider highly unlikely.

So this is an unlikely attack. Nonetheless, administrators who have been very sophisticated in their `DN` construction patterns might conceivably be impacted. Versions 2.11.15 and 2.12.6 contain a fix.

As a workaround, developers should review their CA issuing practices.

Attack Parameters

Attack Vector

Network

Can be exploited remotely

Attack Complexity

High

Difficult to exploit

Privileges Required

Low

Basic privileges needed

User Interaction

None

No user interaction needed

Impact Assessment

Confidentiality

Low

Partial data leak

Integrity

Low

Partial data modification

Availability

None

No disruption

CVSS Vector v3.1

Weakness Type (CWE)

CWE-295 Improper Certificate Validation

CWE-287 Improper Authentication

Vulnerable Products 2

Configuration	From (including)	Up to (excluding)
Linuxfoundation Nats-Server cpe:2.3:a:linuxfoundation:nats-server::::::::	—	`2.11.15`
Linuxfoundation Nats-Server cpe:2.3:a:linuxfoundation:nats-server::::::::	`2.12.0`	`2.12.6`