NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

CVE-2026-33248 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

Background

NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.

One authentication model supported is mTLS, deriving the NATS client identity from properties of the TLS Client Certificate.

Problem Description

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.

Affected Versions

Fixed in nats-server 2.12.6 & 2.11.15

Workarounds

Developers should review their CA issuing practices.

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2026-03-24 21:51:08 UTC
Updated
2026-03-27 22:10:39 UTC
GitHub reviewed
2026-03-24 21:51:08 UTC
NVD published
2026-03-25 21:16:47 UTC

EPSS Score

Score Percentile
0.02% 4.59%

CVSS Scores

Base score Version Severity Vector
4.2 3.1 —
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.

Identifiers

Type Value
GHSA GHSA-3f24-pcvm-5jqc ↗
CVE CVE-2026-33248 ↗

CWEs

CWE id Name
CWE-287 Improper Authentication
CWE-295 Improper Certificate Validation

Affected packages (3)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go github.com/nats-io/nats-server/v2 < 2.11.15 2.11.15 —
go github.com/nats-io/nats-server/v2 >= 2.12.0-RC.1, < 2.12.6 2.12.6 —
go github.com/nats-io/nats-server > 0 — —

References

cvelogic Threat Intelligence