🛡️ CVE-2020-26521 — jwt

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-476 OSV
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Nil dereference in NATS JWT, DoS of nats-server

Problem Description

The 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.

A 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.

The NATS Server is known to be impacted by this.

Affected versions

JWT library

  • all versions prior to 1.1.0

NATS Server

  • Version 2 prior to 2.1.9

Impact

JWT library

  • Programs would nil dereference and panic, aborting execution by default.

NATS server

  • Denial of Service caused by process termination

Workaround

If your NATS servers do not trust any accounts which are managed by untrusted entities, then malformed User credentials are unlikely to be encountered.

Solution

Upgrade the JWT dependency in any application using it.

Upgrade the NATS server if using NATS Accounts.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Weakness class

CVE-2020-26521 is classified as CWE-476: NULL Pointer Dereference. A pointer that can be null is used without a check, crashing the process.

Affected software

CVE-2020-26521 is recorded against 1 package.

  • github.com/nats-io/jwt

Timeline and source

Published on 11 February 2022 and last revised on 4 February 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Web)
advisories.nats.io (Web)
github.com (Package)
github.com (Web)
lists.fedoraproject.org (Web)
pkg.go.dev (Web)
www.openwall.com (Web)

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-476
Public Exploit ✅ No
Source OSV
Published 2022-02-11
Updated 2026-08-12
Modified 2026-02-04

Affected Packages

Software From version Fixed in
github.com/nats-io/jwt — —

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