Firebase PHP-JWT < 6.0.0 - Algorithm Confusion
In Firebase PHP-JWT before 6.0.0, an algorithm-confusion issue (e.g., RS256 / HS256) exists via the kid (aka Key ID) header, when multiple types of keys are loaded in a key ring. This allows an attacker to forge tokens that validate under the incorrect key. This may or may not be exploitable in WordPress plugins and themes using the library.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | firebase/php-jwt | < 6.0.0 | 6.0.0 |
| WordPress plugin | JWT Auth – WordPress JSON Web Token Authentication | <= 2.1.0 | 2.1.1 |
References
- https://nvd.nist.gov/vuln/detail/CVE-2021-46743
- https://github.com/firebase/php-jwt/issues/351
- https://github.com/FriendsOfPHP/security-advisories/blob/master/firebase/php-jwt/CVE-2021-46743.yaml
- https://github.com/firebase/php-jwt
- https://github.com/firebase/php-jwt/releases/tag/v6.0.0
- https://www.wordfence.com/threat-intel/vulnerabilities/id/8aa0fffa-475e-4227-9ab1-17ca6fcce529?source=api-prod
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N- Weakness (CWE)
CWE-347, CWE-843- Platform
- Composer, WordPress
- Package
firebase/php-jwt, JWT Auth – WordPress JSON Web Token Authentication- Disclosed
- 30.03.2022
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-8xf4-w7qw-pjjw - CC BY 4.0
Wordfence Intelligence - 8aa0fffa-475e-4227-9ab1-17ca6fcce529 - Wordfence Intelligence
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Vulnerability history: firebase/php-jwt
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 03.2022 07.2025
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- Low 1
Disclosures per year
- 2022: 1
- 2023: 0
- 2024: 1
- 2025: 1
- 2026: 0
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Firebase PHP-JWT < 6.0.0 - Algorithm Confusion this entry
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