CVE-2026-27932
Published: 03 March 2026
Summary
CVE-2026-27932 is a high-severity Allocation of Resources Without Limits or Throttling (CWE-770) vulnerability in Hsiaoming Joserfc. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 14.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
This control implements explicit throttling on session allocation, addressing the weakness of allocating resources without limits.
Plan testing exercises resource allocation limits and throttling during simulated failures, directly addressing weaknesses that allow unbounded resource use.
Contingency plan updates ensure recovery strategies address unbounded resource allocation, making it harder for attackers to exploit lack of throttling to cause prolonged outages.
Provides continuity when unbounded resource allocation at the primary site leads to exhaustion and downtime.
Alternate services allow operations to continue when primary allocation of resources lacks limits or throttling.
Explicit planning of security-related actions requires defining limits, windows, and resource allocations, making allocation without throttling far less likely.
Measures of performance include tracking allocation behavior and throttling effectiveness, reducing the window for resource exhaustion attacks.
Imposes an inactivity-based limit on network resource allocation, throttling the number of concurrently held connections.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability enables remote unauthenticated exploitation of public-facing apps (T1190) via crafted JWE input that triggers algorithmic complexity leading to application resource exhaustion/DoS (T1499.004).
NVD Description
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. In 1.6.2 and earlier, a resource exhaustion vulnerability in joserfc allows an unauthenticated attacker to cause a Denial of Service (DoS) via…
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CPU exhaustion. When the library decrypts a JSON Web Encryption (JWE) token using Password-Based Encryption (PBES2) algorithms, it reads the p2c (PBES2 Count) parameter directly from the token's protected header. This parameter defines the number of iterations for the PBKDF2 key derivation function. Because joserfc does not validate or bound this value, an attacker can specify an extremely large iteration count (e.g., 2^31 - 1), forcing the server to expend massive CPU resources processing a single token. This vulnerability exists at the JWA layer and impacts all high-level JWE and JWT decryption interfaces if PBES2 algorithms are allowed by the application's policy.
Deeper analysisAI
CVE-2026-27932 is a resource exhaustion vulnerability in the joserfc Python library, versions 1.6.2 and earlier. The flaw arises during decryption of JSON Web Encryption (JWE) tokens using Password-Based Encryption (PBES2) algorithms, where the library reads the p2c (PBES2 Count) parameter directly from the token's protected header without validation or bounding. An attacker can specify an extremely large iteration count, such as 2^31 - 1, forcing excessive CPU consumption in the PBKDF2 key derivation function and causing denial of service (DoS). This issue resides at the JWA layer and affects all high-level JWE and JWT decryption interfaces if PBES2 algorithms are allowed by the application's policy. It is rated 7.5 on CVSS v3.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) and maps to CWE-770 (Allocation of Resources Without Limits or Throttling).
An unauthenticated attacker with network access can exploit this vulnerability remotely with low complexity and no user interaction or privileges required. By crafting and submitting a malicious JWE token with a high p2c value, the attacker triggers massive CPU resource exhaustion on the target server during a single token processing attempt, leading to DoS.
Mitigation details are provided in the joserfc security advisory at https://github.com/authlib/joserfc/security/advisories/GHSA-w5r5-m38g-f9f9 and a fix commit at https://github.com/authlib/joserfc/commit/696a9611ab982c45ee2190ed79ca8e1d8e09398f. Security practitioners should upgrade to a patched version of joserfc and review application policies to restrict or disable PBES2 algorithms where feasible.
Details
- CWE(s)