CVE-2022-29217 in PyJWT
Summary
by MITRE • 05/24/2022
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.
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Analysis
by VulDB Data Team • 03/05/2025
The vulnerability identified as CVE-2022-29217 affects the PyJWT Python library, which implements the JSON Web Token standard defined in RFC 7519. This security flaw arises from the library's default behavior of accepting multiple JWT signing algorithms without explicit application-level restriction. The core issue stems from the fact that JWT tokens can contain a header specifying which signing algorithm was used to create the token, and the PyJWT library allows attackers to manipulate this selection. When applications fail to explicitly define which algorithms are acceptable for token verification, the library defaults to accepting all available algorithms, including potentially insecure ones.
The technical implementation of this vulnerability is rooted in the library's algorithm validation mechanism. Applications using PyJWT must explicitly specify which signing algorithms they accept during token decoding operations. When developers use `jwt.algorithms.get_default_algorithms()` without proper validation, they inadvertently enable support for all available algorithms including those that may be vulnerable to specific attack vectors. This design flaw creates a potential security risk where an attacker could submit a JWT token signed with an algorithm that allows for signature forgery or bypasses authentication mechanisms. The vulnerability is classified as a cryptographic weakness that violates the principle of least privilege in security implementations.
The operational impact of this vulnerability extends beyond simple authentication bypasses, as it can lead to complete system compromise when applications rely on JWT tokens for access control. Attackers exploiting this issue can potentially manipulate JWT tokens to gain unauthorized access to protected resources, especially in environments where applications are configured to accept multiple algorithms. This vulnerability particularly affects systems where the default algorithm set is used without explicit validation, creating a pathway for malicious actors to exploit the trust relationship between the authentication system and the JWT token verification process. The risk is amplified in scenarios where applications handle sensitive data or perform privileged operations based on JWT token validation.
Security practitioners should address this vulnerability by upgrading to PyJWT version 2.4.0 or later, which includes patches specifically designed to prevent automatic acceptance of insecure algorithms. The recommended mitigation strategy involves implementing explicit algorithm whitelisting during token decoding operations, ensuring that only known-safe algorithms are accepted. This approach aligns with the principle of secure coding practices and follows the guidance provided in the CWE-327 vulnerability classification, which addresses the use of weak cryptographic algorithms. Organizations should also implement the ATT&CK technique T1566.001 for credential access, ensuring that JWT token validation is properly configured to prevent algorithm confusion attacks. The workaround of explicit algorithm specification serves as a critical defense-in-depth measure that should be implemented immediately, regardless of the upgrade timeline, to protect against potential exploitation of this cryptographic weakness.