CVE-2026-33248: Github.com/nats io/nats server/v2 Authentication Bypass Vulnerability
MODERATECVE-2026-33248 is a MODERATE (CVSS 4.2) authentication bypass vulnerability (CWE-287: Improper Authentication) affecting Github.com/nats io/nats server/v2 libraries in the Go ecosystem. The issue involves nats has mtls verify_and_map authentication bypass via incorrect subject dn matching. Remediation is available by upgrading affected packages to version 2.11.15, 2.12.6.
CVE-2026-33248 at a Glance
Security Impact
CVSS: 4.2
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N).
How to Fix CVE-2026-33248
To remediate this vulnerability, upgrade all affected Github.com/nats io/nats server/v2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
Upgrade github.com/nats-io/nats-server/v2 to 2.11.15Upgrade github.com/nats-io/nats-server/v2 to 2.12.6Upgrade github.com/nats-io/nats-server to Latest secure releaseRun the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/nats-io/nats-server/v2How to Check if You Are Affected
To determine whether your application is affected by CVE-2026-33248, inspect your project dependencies for Github.com/nats io/nats server/v2:
inspect dependencies for github.com/nats-io/nats-server/v2Analyze the terminal output to locate any version of Github.com/nats io/nats server/v2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.11.15), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-287: Improper Authentication, where when an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. In Github.com/nats io/nats server/v2, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-33248 Affected Github.com/nats io/nats server/v2 Versions
3 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/nats-io/nats-server/v2
|
Go |
< 2.11.15
|
2.11.15
|
|
github.com/nats-io/nats-server/v2
|
Go |
≥ 2.12.0-RC.1
< 2.12.6
|
2.12.6
|
|
github.com/nats-io/nats-server
|
Go |
|
|
References
Frequently Asked Questions
What is CVE-2026-33248?
Which Github.com/nats io/nats server/v2 versions are affected?
What version fixes CVE-2026-33248?
Is github.com/nats-io/nats-server/v2 affected?
Is github.com/nats-io/nats-server affected?
What is the CVSS score of CVE-2026-33248?
What CWE is associated with CVE-2026-33248?
How can I check Go dependencies for CVE-2026-33248?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-3f24-pcvm-5jqc",
"modified" : "2026-03-27T22:10:38Z",
"published" : "2026-03-24T21:51:08Z",
"aliases" : [ "CVE-2026-33248" ],
"summary" : "NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching",
"details" : "### Background\n\nNATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.\n\nOne authentication model supported is mTLS, deriving the NATS client identity from properties of the TLS Client Certificate.\n\n### Problem Description\n\nWhen 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.\n\nThis does require a valid certificate from a CA already trusted for client certificates, and `DN` naming patterns which the NATS maintainers consider highly unlikely.\n\nSo this is an unlikely attack. Nonetheless, administrators who have been very sophisticated in their `DN` construction patterns might conceivably be impacted.\n\n### Affected Versions\n\nFixed in nats-server 2.12.6 & 2.11.15\n\n### Workarounds\n\nDevelopers should review their CA issuing practices.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/nats-server/v2"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "2.11.15"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/nats-server/v2"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.12.0-RC.1"
}, {
"fixed" : "2.12.6"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/nats-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/nats-io/nats-server/security/advisories/GHSA-3f24-pcvm-5jqc"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33248"
}, {
"type" : "WEB",
"url" : "https://advisories.nats.io/CVE/secnote-2026-13.txt"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/nats-io/nats-server"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-287", "CWE-295" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-03-24T21:51:08Z",
"nvd_published_at" : "2026-03-25T21:16:47Z"
}
}