CVE-2026-119284 in joserfc
Summary
by MITRE • 10/30/2026
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.
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Analysis
by VulDB Data Team • 10/30/2026
The vulnerability identified within the joserfc Python library represents a significant resource exhaustion flaw rooted in the order of operations during JSON Web Signature deserialization. Specifically, this issue affects versions prior to 1.7.6 and involves the handling of compact JWS serialization formats. The core technical deficiency lies in the implementation of the deserialize_compact function, which performs memory allocation via bytes.split() before validating whether the input data exceeds predefined aggregate segment-size limits. This sequencing error means that when an attacker supplies a maliciously crafted token with large segments, the library immediately creates copies of the header, payload, and signature components in memory. Only after these allocations have occurred does the validation logic trigger an ExceededSizeError to reject the oversized input.
This architectural flaw leads directly to a denial-of-service condition by exhausting available process memory. Even though the cryptographic verification would ultimately fail due to the invalid size or malformed structure of the token, the damage is already done at the resource allocation stage. An attacker can exploit this behavior by sending requests containing compact JWS tokens with significantly enlarged segments. Each such request forces the server to allocate memory proportional to the supplied token size before discarding it. By repeatedly submitting these oversized payloads, an adversary can rapidly deplete system resources, leading to application crashes or unresponsiveness for legitimate users. This constitutes a classic resource exhaustion vulnerability where the cost of processing invalid input is disproportionately high compared to valid inputs.
From a classification perspective, this issue aligns with CWE-789: Memory Allocation with Excessive Size, as it involves allocating memory based on attacker-controlled data without sufficient prior validation. Furthermore, in the context of adversarial tactics, this vulnerability facilitates availability attacks consistent with MITRE ATT&CK technique T1499: Endpoint Denial of Service or potentially T1498: Network Denial of Service depending on whether the impact is localized to a single process or affects broader network services through resource starvation. The failure to enforce size limits before processing allows for efficient amplification attacks against systems relying on this library for authentication or data integrity verification.
To mitigate this vulnerability, organizations must immediately upgrade joserfc to version 1.7.6 or later, where the deserialization logic has been corrected to validate segment sizes prior to memory allocation. In environments where upgrading is not immediately feasible, implementing a strict input validation layer at the network perimeter can help filter out excessively large tokens before they reach the application server. Additionally, configuring resource limits such as maximum request body size and process memory caps via web servers or container orchestration tools can provide an additional layer of defense against denial-of-service attempts. Regular security audits focusing on cryptographic library implementations are recommended to identify similar ordering flaws in other JOSE-related code paths.