How severe is CVE-2026-33248?

CVE-2026-33248 has a CVSS 3.x base score of 4.2, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-33248 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33248?

CVE-2026-33248 affects Linuxfoundation Nats-server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33248?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-33248 have an EU (EUVD) identifier?

Yes. CVE-2026-33248 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-15999.

When was CVE-2026-33248 published?

CVE-2026-33248 was published on 2026-03-25 and last updated on 2026-06-17.

CVE-2026-33248

CVE-2026-33248 is a medium-severity vulnerability in Linuxfoundation Nats-server with a CVSS 3.x base score of 4.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: Medium (CVSS 3.x base score 4.2)
EPSS exploit prediction: 0% (4th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-15999
Weakness: CWE-287
Affected product: Linuxfoundation Nats-server
Published: 2026-03-25
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-33248?: 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.
How severe is CVE-2026-33248?: CVE-2026-33248 has a CVSS 3.x base score of 4.2, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-33248 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33248?: CVE-2026-33248 affects Linuxfoundation Nats-server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33248?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33248 have an EU (EUVD) identifier?: Yes. CVE-2026-33248 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-15999.
When was CVE-2026-33248 published?: CVE-2026-33248 was published on 2026-03-25 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*

More vulnerabilities in Linuxfoundation Nats-server

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CVE-2026-33218 — High (CVSS 7.5): NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions…
CVE-2026-29785 — High (CVSS 7.5): NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions…

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Other CWE-287 (Improper Authentication) vulnerabilities

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CVE-2026-42822 — Critical (CVSS 10.0): Improper authentication in Azure Local Disconnected Operations allows an unauthorized attacker to elevate privileges…
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