CVE-2022-29217 is a vulnerability identified in the PyJWT library, a widely used Python implementation of JSON Web Tokens (JWT) as defined by RFC 7519. JWTs are commonly used for securely transmitting information between parties as a JSON object, and they rely on cryptographic signing algorithms to ensure the integrity and authenticity of the token. PyJWT supports multiple signing algorithms, and the library allows the application to specify which algorithms are accepted when decoding tokens. The vulnerability arises when an application uses the default setting `jwt.algorithms.get_default_algorithms()` without explicitly restricting the accepted algorithms. This default includes some cryptographic algorithms considered broken or risky (CWE-327), which can be exploited by an attacker who crafts a JWT token specifying a weak or insecure signing algorithm. By doing so, the attacker may bypass signature verification, potentially allowing token forgery or manipulation. The issue affects PyJWT versions from 1.5.0 up to but not including 2.4.0. The recommended mitigation is to upgrade to version 2.4.0 or later, where the vulnerability is patched. Alternatively, applications should explicitly specify and restrict the accepted algorithms when decoding JWTs rather than relying on the default set. This vulnerability does not require user interaction or authentication to exploit, but it does require the attacker to submit a crafted JWT token to the application. There are no known exploits in the wild reported to date. The vulnerability primarily impacts the confidentiality and integrity of systems relying on PyJWT for authentication or authorization mechanisms, as compromised tokens could lead to unauthorized access or privilege escalation.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on PyJWT for securing APIs, web applications, or microservices architectures. Exploitation could allow attackers to forge JWT tokens, bypass authentication controls, and gain unauthorized access to sensitive data or systems. This could lead to data breaches, unauthorized transactions, or disruption of services. Sectors such as finance, healthcare, government, and critical infrastructure that use JWT for identity and access management are particularly at risk. The vulnerability undermines the integrity and confidentiality of authentication tokens, potentially enabling lateral movement within networks or privilege escalation. Given the widespread use of Python and PyJWT in modern web applications, the scope of affected systems is broad. However, the absence of known exploits in the wild suggests that exploitation is not yet widespread, though the risk remains high if unpatched. Organizations failing to upgrade or explicitly restrict algorithms expose themselves to potential compromise, regulatory non-compliance, and reputational damage.

1. Immediate upgrade of PyJWT to version 2.4.0 or later, where the vulnerability is patched. 2. Review all applications using PyJWT to ensure that the decoding of JWT tokens explicitly specifies accepted algorithms rather than relying on the default set. For example, use `jwt.decode(token, key, algorithms=['HS256'])` to restrict to secure algorithms. 3. Conduct code audits to identify any instances where `jwt.algorithms.get_default_algorithms()` or similar default settings are used and replace them with explicit algorithm lists. 4. Implement additional token validation layers such as token expiration checks, issuer validation, and audience restrictions to reduce the risk of token misuse. 5. Monitor application logs for suspicious JWT tokens or authentication anomalies that could indicate attempted exploitation. 6. Educate developers and security teams about secure JWT handling practices and the risks of using weak cryptographic algorithms. 7. For critical systems, consider implementing Web Application Firewalls (WAFs) or API gateways that can enforce strict JWT validation policies. These measures go beyond generic advice by focusing on explicit algorithm restriction, code auditing, and layered validation controls.