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CVE-2020-26521

The JWT library in NATS nats-server before 2.1.9 allows a denial of service (a nil dereference in Go code).

Summary

Vulnerability reported (CVE-2020-26521). Risk of unauthorized operations or information disclosure.

Original description

The description as published by the source.

(This advisory is canonically )

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.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2020-26521 has been found.
Risk of unauthorized operations or information disclosure.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "CVE-2020-26521" on the vendor's site.

CVE-2020-26521
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) has been reported.

📍 Affected scope

Check the vendor advisory for the affected versions.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで影響コンポーネントを特定する。

  2. 2
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Go github.com/nats-io/jwt
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.1.0"}]}]
Go github.com/nats-io/nats-server/v2
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.1.9"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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