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 15.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SI-10 (Information Input Validation).
Deeper analysis
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-9344
Vulnerability details
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…
more
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.
- CWE(s)
Related Threats
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).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Remediates the specific resource exhaustion flaw in joserfc by applying patches that bound the p2c iteration count during PBES2 decryption.
Validates untrusted inputs such as the p2c parameter from JWE token headers to enforce bounds and prevent CPU exhaustion in PBKDF2 key derivation.
Implements denial-of-service protections to mitigate resource exhaustion attacks from malicious JWE tokens with excessive iteration counts.