CVE-2017-11424
HighSummary
In PyJWT versions 1.5.0 and below, the `invalid_strings` check in `HMACAlgorithm.prepare_key` does not account for all PEM encoded public keys. Specifically, the PKCS1 PEM encoded format is allowed, enabling symmetric/asymmetric key confusion attacks.
Risk Assessment
An attacker could craft fake JWTs, leading to serious security vulnerabilities in applications using PKCS1 PEM keys. This could result in unauthorized access to user data.
Recommendation
It is recommended to update PyJWT to a version above 1.5.0 to mitigate this vulnerability. Additionally, an audit of the public keys used in the application should be conducted.
Other vulnerabilities in PyJWT
See all- CVE-2026-48526High
PyJWT library in Python prior to 2.13.0 does not validate the use of JSON Web Keys in HMAC algorithm, allowing an attacker to use the issuer's public key as the HMAC secret key.
- CVE-2026-32597High
PyJWT before version 2.12.0 does not validate the crit (Critical) Header Parameter defined in RFC 7515. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it, violating the MUST requirement in the RFC.
Original NVD description (English source)
In PyJWT 1.5.0 and below the `invalid_strings` check in `HMACAlgorithm.prepare_key` does not account for all PEM encoded public keys. Specifically, the PKCS1 PEM encoded format would be allowed because it is prefaced with the string `-----BEGIN RSA PUBLIC KEY-----` which is not accounted for. This enables symmetric/asymmetric key confusion attacks against users using the PKCS1 PEM encoded public keys, which would allow an attacker to craft JWTs from scratch.