Description
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. In versions from 1.3.3 to before 1.3.5 and from 1.4.0 to before 1.4.2, the ExceededSizeError exception messages are embedded with non-decoded JWT token parts and may cause Python logging to record an arbitrarily large, forged JWT payload. In situations where a misconfigured — or entirely absent — production-grade web server sits in front of a Python web application, an attacker may be able to send arbitrarily large bearer tokens in the HTTP request headers. When this occurs, Python logging or diagnostic tools (e.g., Sentry) may end up processing extremely large log messages containing the full JWT header during the joserfc.jwt.decode() operation. The same behavior also appears when validating claims and signature payload sizes, as the library raises joserfc.errors.ExceededSizeError() with the full payload embedded in the exception message. Since the payload is already fully loaded into memory at this stage, the library cannot prevent or reject it. This issue has been patched in versions 1.3.5 and 1.4.2.
EPSS Score:
0%
Comprehensive Technical Analysis of EUVD-2025-198059
1. Vulnerability Assessment and Severity Evaluation
The vulnerability described in EUVD-2025-198059 pertains to the joserfc Python library, which is used for JSON Object Signing and Encryption (JOSE) standards. The issue arises from the way the library handles ExceededSizeError exceptions, which can lead to the logging of arbitrarily large, forged JWT payloads. This can result in significant resource consumption and potential denial of service (DoS) conditions.
Severity Evaluation:
- CVSS Base Score: 9.2
- CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
The high base score indicates a critical vulnerability due to the potential for high availability impact (VA:H) and high severity impact (SA:H). The attack vector is network-based (AV:N), requires low attack complexity (AC:L), and does not need any privileges (PR:N) or user interaction (UI:N).
2. Potential Attack Vectors and Exploitation Methods
Attack Vectors:
- Network-Based Attack: An attacker can send HTTP requests with arbitrarily large JWT tokens in the headers.
- Logging Systems: The vulnerability can be exploited by targeting logging systems that process and store these large JWT payloads.
Exploitation Methods:
- Forged JWT Tokens: An attacker can craft JWT tokens with excessively large payloads and send them to the target application.
- Resource Exhaustion: The large payloads can exhaust memory and storage resources, leading to a denial of service.
- Log Poisoning: The large log entries can overwhelm logging systems, making it difficult to diagnose and respond to the attack.
3. Affected Systems and Software Versions
Affected Versions:
joserfcversions from 1.3.3 to before 1.3.5joserfcversions from 1.4.0 to before 1.4.2
Affected Systems:
- Any Python web application using the vulnerable versions of
joserfc. - Systems with misconfigured or absent production-grade web servers in front of the application.
4. Recommended Mitigation Strategies
Immediate Mitigation:
- Upgrade
joserfcLibrary: Upgrade to versions 1.3.5 or 1.4.2, which include patches for this vulnerability. - Limit JWT Token Size: Implement size limits on JWT tokens in HTTP request headers.
- Rate Limiting: Implement rate limiting to prevent excessive requests.
Long-Term Mitigation:
- Proper Web Server Configuration: Ensure that a properly configured production-grade web server is in place to handle and filter requests before they reach the application.
- Monitoring and Alerts: Set up monitoring and alerts for unusually large log entries or high resource usage.
- Regular Audits: Conduct regular security audits and code reviews to identify and mitigate similar vulnerabilities.
5. Impact on European Cybersecurity Landscape
The vulnerability poses a significant risk to European organizations using the joserfc library, particularly those handling sensitive data or providing critical services. The potential for denial of service attacks can disrupt operations and lead to financial losses. The widespread use of JWT tokens in authentication and authorization mechanisms amplifies the impact, making it crucial for organizations to address this vulnerability promptly.
6. Technical Details for Security Professionals
Technical Overview:
- Exception Handling: The
ExceededSizeErrorexception injoserfcembeds non-decoded JWT token parts in its messages, leading to the logging of large payloads. - Memory Consumption: The payload is fully loaded into memory before the exception is raised, making it impossible to prevent or reject at that stage.
- Logging Impact: Logging systems like Sentry may process extremely large log messages, exacerbating the issue.
Code Analysis:
- Vulnerable Code: The issue arises in the
joserfc.jwt.decode()operation and when validating claims and signature payload sizes. - Patch Details: The patches in versions 1.3.5 and 1.4.2 address the exception handling to prevent the embedding of large payloads in exception messages.
References:
- GitHub Advisory
- Commit 63932f169d924caffafa761af2122b82059017f7
- Commit 673c8743fd0605b0e1de6452be6cba75f44e466b
- joserfc GitHub Repository
- Release 1.3.5
- Release 1.4.2
By addressing this vulnerability promptly and implementing robust mitigation strategies, organizations can significantly reduce the risk of exploitation and ensure the security and reliability of their systems.