CVE-2026-33248 | NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

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.

Published: 2026-03-25 Last update: 2026-03-26 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33248 is rated Low Risk (18.6/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.02%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-33248

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-26 — 0.02% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33248

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.2 3.1 MEDIUM
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.
 1.6 2.5 [email protected]

Weakness enumeration for CVE-2026-33248

GitHub Security Advisory for CVE-2026-33248

GHSA-3f24-pcvm-5jqc · Severity: medium · Ecosystem: go — NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

OS Trackers for CVE-2026-33248

vendor priority summary link
alpine — CVE-2026-33248: 1 source package rows (nats-server); 39 state rows across 2 repos (3.23-community, edge-community); fixed 2, open 37. https://security.alpinelinux.org/vuln/CVE-2026-33248
debian not yet assigned CVE-2026-33248 not yet assigned priority: Debian including 1 source packages (nats-server), 4 status rows across 4 suites (bookworm, forky, sid, trixie): open 2, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-33248
redhat medium — https://access.redhat.com/security/cve/CVE-2026-33248
suse medium — https://www.suse.com/security/cve/CVE-2026-33248/
ubuntu medium CVE-2026-33248 medium priority: Ubuntu including 1 source packages (nats-server), 4 status rows across 4 suites (jammy, noble, questing, upstream): needs-triage 3, DNE 1. https://ubuntu.com/security/CVE-2026-33248

Affected software / configurations for CVE-2026-33248

Vendor Product Version Raw CPE
linuxfoundation nats-server < 2.11.15 cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*
linuxfoundation nats-server >= 2.12.0, < 2.12.6 cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*

References for CVE-2026-33248

cvelogic Threat Intelligence