Affected: jpadilla pyjwt

PyJWT is a Python implementation of RFC 7519. PyJWT supports multiple different JWT signing algorithms. With JWT, an attacker submitting the JWT token can choose the used signing algorithm. The PyJWT library requires that the application chooses what algorithms are supported. The application can specify `jwt.algorithms.get_default_algorithms()` to get support for all algorithms, or specify a single algorithm. The issue is not that big as `algorithms=jwt.algorithms.get_default_algorithms()` has to be used. Users should upgrade to v2.4.0 to receive a patch for this issue. As a workaround, always be explicit with the algorithms that are accepted and expected when decoding.

Affected: PyPI: pyjwt

### Impact _What kind of vulnerability is it? Who is impacted?_

Disclosed by Aapo Oksman (Senior Security Specialist, Nixu Corporation).

> PyJWT supports multiple different JWT signing algorithms. With JWT, an > attacker submitting the JWT token can choose the used signing algorithm. > > The PyJWT library requires that the application chooses what algorithms > are supported. The application can specify > "jwt.algorithms.get_default_algorithms()" to get support for all > algorithms. They can also specify a single one of them (which is the > usual use case if calling jwt.decode directly. However, if calling > jwt.decode in a helper function, all algorithms might be enabled.) > > For example, if the user chooses "none" algorithm and the JWT checker > supports that, there will be no signature checking. This is a common > security issue with some JWT implementations. > > PyJWT combats this by requiring that the if the "none" algorithm is > used, the key has to be empty. As the key is given by the application > running the checker, attacker cannot force "none" cipher to be used. > > Similarly with HMAC (symmetric) algorithm, PyJWT checks that the key is > not a public key meant for asymmetric algorithm i.e. HMAC cannot be used > if the key begins with "ssh-rsa". If HMAC is used with a public key, the > attacker can just use the publicly known public key to sign the token > and the checker would use the same key to verify. > > From PyJWT 2.0.0 onwards, PyJWT s…

Affected: PyPI: pyjwt

PyJWT is a Python implementation of RFC 7519. PyJWT supports multiple different JWT signing algorithms. With JWT, an attacker submitting the JWT token can choose the used signing algorithm. The PyJWT library requires that the application chooses what algorithms are supported. The application can specify `jwt.algorithms.get_default_algorithms()` to get support for all algorithms, or specify a single algorithm. The issue is not that big as `algorithms=jwt.algorithms.get_default_algorithms()` has to be used. Users should upgrade to v2.4.0 to receive a patch for this issue. As a workaround, always be explicit with the algorithms that are accepted and expected when decoding.