CVE-2025-61152 affects the python-jose library, a popular Python implementation for JSON Web Token (JWT) handling, up to version 3.3.0. The vulnerability arises because the library permits JWT tokens with the 'alg' header set to 'none' to be decoded and accepted without any cryptographic signature verification. JWT tokens typically include a signature to ensure the integrity and authenticity of the claims they carry. However, when 'alg=none' is accepted, the token is treated as unsigned, allowing an attacker to craft arbitrary tokens with manipulated claims, such as setting 'is_admin=true' or other privilege escalation flags. This can lead to unauthorized access or privilege escalation in applications relying on python-jose for authentication and authorization. The root cause is that the library does not enforce rejection of 'alg=none' tokens by default, leaving it to developers to explicitly disable or reject such tokens. The vulnerability is exploitable only if the application does not set 'verify_signature' to false, which disables signature verification altogether and is generally not recommended. The CVSS v3.1 base score is 6.5, indicating a medium severity with network attack vector, low attack complexity, no privileges required, and no user interaction needed. The impact primarily affects confidentiality and integrity, as unauthorized users can gain elevated privileges or access sensitive data. No patches or fixes are currently linked, and no known exploits have been reported in the wild. The CWE classification is CWE-269 (Improper Privilege Management), highlighting the risk of unauthorized privilege escalation due to improper token validation.

For European organizations, this vulnerability poses a significant risk if python-jose is used in authentication or authorization workflows without proper configuration. Attackers could exploit this flaw to bypass authentication controls, escalate privileges, and gain unauthorized access to sensitive systems or data. This could lead to data breaches, compliance violations (e.g., GDPR), and damage to organizational reputation. The impact is particularly critical for sectors handling sensitive personal data or critical infrastructure, such as finance, healthcare, and government services. Since the vulnerability allows forging tokens with arbitrary claims, attackers might impersonate privileged users or administrators, potentially leading to lateral movement within networks and further compromise. The absence of known exploits suggests limited current risk, but the ease of exploitation and the widespread use of JWTs in modern web applications mean that the threat could escalate rapidly if weaponized. Organizations relying on python-jose should assess their exposure and remediate promptly to prevent potential exploitation.

1. Immediately audit all applications using python-jose for JWT validation to determine if they accept tokens with 'alg=none' or disable signature verification. 2. Ensure that the application explicitly rejects JWT tokens with 'alg=none' by configuring the library or implementing custom validation logic. 3. Avoid setting 'verify_signature' to false; signature verification must always be enabled in production environments. 4. Update to a patched version of python-jose once available or apply community patches that enforce rejection of 'alg=none' tokens. 5. Implement additional layers of authentication and authorization checks beyond JWT claims to reduce reliance on token integrity alone. 6. Monitor logs for suspicious authentication attempts involving tokens with 'alg=none' or unusual claims. 7. Educate developers about secure JWT handling practices, emphasizing the risks of accepting unsigned tokens. 8. Consider using alternative JWT libraries that enforce stricter validation policies if python-jose cannot be updated promptly. 9. Conduct penetration testing focused on JWT authentication to identify potential exploitation paths. 10. Maintain an incident response plan to quickly address any detected misuse of forged tokens.