CVE-2020-26521: Github.com/nats io/jwt Denial of Service Vulnerability
HIGHCVE-2020-26521 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-476: NULL Pointer Dereference) affecting Github.com/nats io/jwt libraries in the Go ecosystem. The issue involves nil dereference in nats jwt, dos of nats-server. Remediation is available by upgrading affected packages to version 1.1.0.
CVE-2020-26521 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
How to Fix CVE-2020-26521
To remediate this vulnerability, upgrade all affected Github.com/nats io/jwt 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/jwt to 1.1.0Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/nats-io/jwtHow to Check if You Are Affected
To determine whether your application is affected by CVE-2020-26521, inspect your project dependencies for Github.com/nats io/jwt:
inspect dependencies for github.com/nats-io/jwtAnalyze the terminal output to locate any version of Github.com/nats io/jwt in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.1.0), 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-476: NULL Pointer Dereference, where the product dereferences a pointer that it expects to be valid but is null. In Github.com/nats io/jwt, 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-2020-26521 Affected Github.com/nats io/jwt Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/nats-io/jwt
|
Go |
< 1.1.0
|
1.1.0
|
References
Frequently Asked Questions
What is CVE-2020-26521?
Which Github.com/nats io/jwt versions are affected?
What version fixes CVE-2020-26521?
Is github.com/nats-io/jwt affected?
What is the CVSS score of CVE-2020-26521?
What CWE is associated with CVE-2020-26521?
How can I check Go dependencies for CVE-2020-26521?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-h2fg-54x9-5qhq",
"modified" : "2025-10-03T19:29:57Z",
"published" : "2022-02-11T23:43:13Z",
"aliases" : [ "CVE-2020-26521" ],
"summary" : "Nil dereference in NATS JWT, DoS of nats-server",
"details" : "## Problem Description\n\nThe NATS account system has an Operator trusted by the servers, which signs Accounts, and each Account can then create and sign Users within their account. The Operator should be able to safely issue Accounts to other entities which it does not fully trust.\n\nA malicious Account could create and sign a User JWT with a state not created by the normal tooling, such that decoding by the NATS JWT library (written in Go) would attempt a nil dereference, aborting execution.\n\nThe NATS Server is known to be impacted by this.\n\n\n## Affected versions\n\n#### JWT library\n\n * all versions prior to 1.1.0\n\n#### NATS Server\n\n * Version 2 prior to 2.1.9\n\n\n## Impact\n\n#### JWT library\n\n * Programs would nil dereference and panic, aborting execution by default.\n\n#### NATS server\n\n * Denial of Service caused by process termination\n\n\n## Workaround\n\nIf your NATS servers do not trust any accounts which are managed by untrusted entities, then malformed User credentials are unlikely to be encountered.\n\n\n## Solution\n\nUpgrade the JWT dependency in any application using it.\n\nUpgrade the NATS server if using NATS Accounts.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/jwt"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "1.1.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/nats-io/jwt/security/advisories/GHSA-h2fg-54x9-5qhq"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-26521"
}, {
"type" : "WEB",
"url" : "https://github.com/nats-io/jwt/pull/107"
}, {
"type" : "WEB",
"url" : "https://github.com/nats-io/nats-server/commit/9ff8bcde2e46009e98bd9e88f598af355f62c168"
}, {
"type" : "WEB",
"url" : "https://advisories.nats.io/CVE/CVE-2020-26521.txt"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/nats-io/jwt"
}, {
"type" : "WEB",
"url" : "https://github.com/nats-io/nats-server/commits/master"
}, {
"type" : "WEB",
"url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VT67XCLIIBYRT762SVFBYFFTQFVSM3SI"
}, {
"type" : "WEB",
"url" : "https://pkg.go.dev/vuln/GO-2022-0402"
}, {
"type" : "WEB",
"url" : "http://www.openwall.com/lists/oss-security/2020/11/02/2"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-476" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2021-05-21T21:32:02Z",
"nvd_published_at" : "2020-11-06T08:15:00Z"
}
}