High, CVSS 7.5npmAmendedPublished
json-web-token library is vulnerable to a JWT algorithm confusion attack
CVE-2023-48238 · GHSA-4xw9-cx39-r355
- Affected
- npm json-web-token < 4.0.0
- Fixed in
- 4.0.0· Vendor fix available
- Issue
- The json-web-token library is vulnerable to a JWT algorithm confusion attack. Details On line 86 of the 'index.js' file, the algorithm to use for verifying the signature of the JWT token is taken from the JWT token, which at that point is still unverified and thus shouldn't be trusted. 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 against this library is the RS256 algorithm is in use, however it is a best practice to use that algorithm. PoC Take a server running the following code: Public key recovery First, an attacker needs to recover the public key from the server in any way possible. It is possible to extract this from just two JWT tokens as shown below. Grab two different JWT tokens and utilize the following tool: https://github.com/silentsignal/rsasign2n/blob/release/standalone/jwtforgery.py The tool will generate 4…
Recommended action: Upgrade to 4.0.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.