CVE-2023-48223: fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to version 3.3.2, the fast-jwt library does not properly prevent JWT algorithm confu...

Description

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to version 3.3.2, the fast-jwt library does not properly prevent JWT algorithm confusion for all public key types. The 'publicKeyPemMatcher' in 'fast-jwt/src/crypto.js' does not properly match all common PEM formats for public keys. To exploit this vulnerability, an attacker needs to craft a malicious JWT token containing the HS256 algorithm, signed with the public RSA key of the victim application. This attack will only work if the victim application utilizes a public key containing the `BEGIN RSA PUBLIC KEY` header. Applications using the RS256 algorithm, a public key with a `BEGIN RSA PUBLIC KEY` header, and calling the verify function without explicitly providing an algorithm, are vulnerable to this algorithm confusion attack which allows attackers to sign arbitrary payloads which will be accepted by the verifier. Version 3.3.2 contains a patch for this issue. As a workaround, change line 29 of `blob/master/src/crypto.js` to include a regular expression.

Metrics

CVSS 3.1

5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

0.69%

48.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-20

Affected Software

Vendor	Product	Versions
Nearform	Fast-Jwt	< 3.3.2

References

https://github.com/nearform/fast-jwt/blob/master/src/crypto.js#L29Product
https://github.com/nearform/fast-jwt/releases/tag/v3.3.2Release Notes
https://github.com/nearform/fast-jwt/security/advisories/GHSA-c2ff-88x2-x9pgExploit, Vendor Advisory
https://github.com/nearform/fast-jwt/blob/master/src/crypto.js#L29Product
https://github.com/nearform/fast-jwt/releases/tag/v3.3.2Release Notes
https://github.com/nearform/fast-jwt/security/advisories/GHSA-c2ff-88x2-x9pgExploit, Vendor Advisory

Timeline

Published: Nov 20, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-48223?

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to version 3.3.2, the fast-jwt library does not properly prevent JWT algorithm confusion for all public key types. The 'publicKeyPemMatcher' in 'fast-jwt/src/crypto.js' does not properly match all common PEM formats for public keys. To exploit this vulnerability, an attacker needs to craft a malicious JWT token containing the HS256 algorithm, signed with the public RSA key of the victim application. This attack will only work if the victim application utilizes a public key containing the `BEGIN RSA PUBLIC KEY` header. Applications using the RS256 algorithm, a public key with a `BEGIN RSA PUBLIC KEY` header, and calling the verify function without explicitly providing an algorithm, are vulnerable to this algorithm confusion attack which allows attackers to sign arbitrary payloads which will be accepted by the verifier. Version 3.3.2 contains a patch for this issue. As a workaround, change line 29 of `blob/master/src/crypto.js` to include a regular expression.

How severe is CVE-2023-48223?

CVE-2023-48223 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 0.69% probability of exploitation in the next 30 days.

How do I fix CVE-2023-48223?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.