Description
cjwt is a C JSON Web Token (JWT) Implementation. Algorithm confusion occurs when a system improperly verifies the type of signature used, allowing attackers to exploit the lack of distinction between signing methods. If the system doesn't differentiate between an HMAC signed token and an RS/EC/PS signed token during verification, it becomes vulnerable to this kind of attack. For instance, an attacker could craft a token with the alg field set to "HS256" while the server expects an asymmetric algorithm like "RS256". The server might mistakenly use the wrong verification method, such as using a public key as the HMAC secret, leading to unauthorised access. For RSA, the key can be computed from a few signatures. For Elliptic Curve (EC), two potential keys can be recovered from one signature. This can be used to bypass the signature mechanism if an application relies on asymmetrically signed tokens. This issue has been addressed in version 2.3.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.
EPSS Score:
0%
Comprehensive Technical Analysis of EUVD-2024-52316
1. Vulnerability Assessment and Severity Evaluation
Vulnerability Description: The vulnerability in the cjwt library, a C JSON Web Token (JWT) implementation, arises from algorithm confusion during the verification process. Specifically, the system fails to properly distinguish between different signing methods, such as HMAC and asymmetric algorithms (RS/EC/PS). This confusion can lead to the server using an incorrect verification method, potentially allowing attackers to bypass the signature mechanism and gain unauthorized access.
Severity Evaluation:
The vulnerability has a CVSS Base Score of 9.1, which is considered critical. The scoring vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N indicates the following:
- Attack Vector (AV): Network (N)
- Attack Complexity (AC): Low (L)
- Privileges Required (PR): None (N)
- User Interaction (UI): None (N)
- Scope (S): Unchanged (U)
- Confidentiality (C): High (H)
- Integrity (I): High (H)
- Availability (A): None (N)
This high severity score underscores the critical nature of the vulnerability, which can lead to significant confidentiality and integrity impacts.
2. Potential Attack Vectors and Exploitation Methods
Attack Vectors:
- Algorithm Confusion: An attacker can craft a JWT with the
algfield set to "HS256" while the server expects an asymmetric algorithm like "RS256". The server might mistakenly use the wrong verification method, such as using a public key as the HMAC secret. - Key Recovery: For RSA, the key can be computed from a few signatures. For Elliptic Curve (EC), two potential keys can be recovered from one signature. This can be used to bypass the signature mechanism if an application relies on asymmetrically signed tokens.
Exploitation Methods:
- Token Forgery: An attacker can forge a JWT by manipulating the
algfield to trick the server into using an incorrect verification method. - Signature Bypass: By exploiting the algorithm confusion, an attacker can bypass the signature verification process, leading to unauthorized access.
3. Affected Systems and Software Versions
Affected Software:
- cjwt library versions: All versions prior to 2.3.0
Affected Systems:
- Any system or application that uses the cjwt library for JWT verification and is running a version earlier than 2.3.0.
4. Recommended Mitigation Strategies
Immediate Mitigation:
- Upgrade: Upgrade to cjwt version 2.3.0 or later, which addresses the algorithm confusion issue.
Additional Mitigations:
- Strict Algorithm Validation: Ensure that the JWT verification process strictly validates the
algfield and uses the correct verification method. - Monitoring and Logging: Implement robust monitoring and logging to detect any suspicious activities related to JWT verification.
- Regular Audits: Conduct regular security audits and code reviews to identify and mitigate similar vulnerabilities.
5. Impact on European Cybersecurity Landscape
Impact Assessment:
- Widespread Use: The cjwt library is widely used in various applications, making the vulnerability a significant risk across multiple sectors.
- Critical Infrastructure: Systems relying on JWT for authentication and authorization, especially in critical infrastructure, are at high risk.
- Compliance: Organizations must ensure compliance with relevant regulations and standards, such as GDPR, to protect sensitive data.
Regulatory and Compliance Considerations:
- GDPR: Organizations must ensure that personal data is protected and that any breach is reported within the required timeframe.
- NIS Directive: Critical infrastructure operators must comply with the Network and Information Systems (NIS) Directive to ensure the security and resilience of their systems.
6. Technical Details for Security Professionals
Technical Analysis:
- Algorithm Confusion: The root cause is the lack of proper distinction between HMAC and asymmetric algorithms during JWT verification.
- Key Recovery: For RSA, the key can be computed from a few signatures. For EC, two potential keys can be recovered from one signature, leading to potential bypass of the signature mechanism.
Detection and Response:
- Intrusion Detection Systems (IDS): Implement IDS to detect anomalies in JWT verification processes.
- Incident Response Plan: Develop and maintain an incident response plan to quickly address any detected vulnerabilities or breaches.
Code Review:
- Algorithm Validation: Ensure that the code strictly validates the
algfield and uses the correct verification method. - Unit Tests: Implement unit tests to verify the correct handling of different signing algorithms.
References:
By addressing this vulnerability promptly and implementing robust mitigation strategies, organizations can significantly reduce the risk of unauthorized access and ensure the security of their systems.