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CVE-2026-33248

NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

MEDIUM
4.2
CVSS Score
Published: March 25, 2026 at 08:18 PM UTC
Updated: June 17, 2026 at 10:37 AM UTC
2 products affected across 2 vendorsNats ServerNats Server

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Severity
MEDIUM4.2
Exploit prediction
EPSS 0.1%
SSVC
No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Nats Server· Linuxfoundation
95%
v < 2.11.152.12.0 ≤ v < 2.12.6
Nats Server· Nats Io
60%
v < 2.11.15v < 2.12.6
Affected range stops below 2.11.15, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.12.6, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

x_refsource_CONFIRMVendor Advisory
Source: cverecord
https://github.com/nats-io/nats-server/security/advisories/GHSA-3f24-pcvm-5jqc
x_refsource_MISCVendor Advisory
Source: cverecord
https://advisories.nats.io/CVE/secnote-2026-13.txt

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

4.2MEDIUMGitHub_M
Attack Vector
NETWORK
Complexity
HIGH
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-287CWE-295

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