CVE-2026-102946 in joserfc
Summary
by MITRE • 10/15/2026
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.4, joserfc.jws.deserialize_json() accepts a JWS General JSON Serialization with an empty signatures array as authenticated. The verify_general_json() loop performs no iterations for the empty array and returns success because no signature check failed, allowing an attacker without a signing key to supply an arbitrary payload that relying applications may treat as authentic. The issue affects the General JSON Serialization path; compact JWS and JWT decoding, Flattened JSON serialization, and JWE JSON processing do not follow this vulnerable path. This issue is fixed in version 1.7.4.
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Analysis
by VulDB Data Team • 10/15/2026
The joserfc library serves as a Python implementation of several standards within the JSON Object Signing and Encryption (JOSE) ecosystem, which includes specifications for digital signatures and encryption such as JWS and JWT. A critical security flaw was identified in versions prior to 1.7.4 regarding the handling of General JSON Serialization format for JSON Web Signatures. This specific serialization method allows a signature object to contain multiple independent signatures over the same payload, designed primarily for scenarios where different parties sign the same data independently rather than creating a chain of trust. The vulnerability stems from an incorrect validation logic within the deserialize_json function when processing this general structure.
The technical root cause lies in how the verify_general_json loop processes the array of signature objects associated with the JWS General JSON Serialization. When an attacker submits a payload where the signatures array is empty, the verification loop executes zero iterations because there are no signature objects to validate against. Consequently, the function returns a success status without performing any cryptographic checks or verifying that at least one valid signature exists for the provided content. This logic error effectively treats unsigned data as authenticated, bypassing the fundamental security guarantee of digital signatures which is to ensure integrity and authenticity through asymmetric cryptography.
This vulnerability enables an attacker who does not possess the private signing key to craft arbitrary JSON Web Signature objects with empty signature arrays. Relying applications that utilize joserfc for authentication or authorization decisions may incorrectly interpret these unsigned payloads as legitimate and authentic messages. This misinterpretation can lead to severe operational impacts, including unauthorized access to protected resources, data integrity violations where malicious commands are executed under the guise of a trusted source, and potential privilege escalation if the application relies on JWS claims for identity verification without additional checks. The flaw is specifically isolated to the General JSON Serialization path; compact serialization formats like standard JWS or JWT, as well as Flattened JSON serialization and JWE processing, do not follow this vulnerable code path and remain unaffected by this specific logic error.
From a classification perspective, this issue aligns with CWE-347 Improper Verification of Cryptographic Signature, where the system fails to adequately verify that a digital signature corresponds to its claimed identity or is valid for the submitted data. In terms of attack vectors, it relates to MITRE ATT&CK technique T1608 Linked Objects, as an attacker can manipulate object structures within serialized formats to bypass security controls. The exploitation relies on the application trusting the output of the verification function without ensuring that a signature was actually present and validated, highlighting the importance of explicit checks for non-empty credential sets in cryptographic libraries.
To mitigate this vulnerability, organizations must immediately upgrade joserfc to version 1.7.4 or later, where the logic has been corrected to ensure that at least one valid signature is required for authentication success regardless of the serialization format used. For applications unable to update immediately, defensive coding practices should be implemented by explicitly checking that the signatures array contains elements before considering a JWS object as authenticated. Additionally, developers should review their reliance on JOSE libraries and consider implementing additional validation layers or using alternative libraries with more rigorous default security postures for critical authentication flows. Regular auditing of cryptographic implementation details is essential to prevent similar logic errors in other parts of the application stack that depend on these standards.