CVE-2026-27932
joserfc PBES2 p2c Unbounded Iteration Count enables Denial of Service (DoS)
Reported by github_m · Published March 3, 2026
joserfc is fixed in 1.6.3 (PyPI)
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 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.
Fixed versions
Upgrade to a fixed version or later. Language registries are listed first, then Linux distributions, then vendor products.
| Package | Ecosystem | Fixed in |
|---|---|---|
| joserfc | PyPI | 1.6.3 |
| localstack | Chainguard | 4.14.0-r1 |
| joserfc | hsiaoming | 1.6.2 |
Risk scores
Affected products
| Vendor | Product | Versions |
|---|---|---|
| authlib | joserfc | <= 1.6.2 |
| PyPI | joserfc | 0 |
| chainguard | localstack | 0 |
| authlib | joserfc | 0 |
Timeline
- Mar 2, 2026 CVE Published
- Mar 3, 2026 PoC Published (3 in total, the first dated here)
- Mar 4, 2026 EPSS Score (30 in total, the first dated here)
- Mar 4, 2026 CVE Updated
- Mar 9, 2026 Security Advisory
- Mar 17, 2026 Coalition ESS Score (2 in total, the first dated here)
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References
- https://github.com/authlib/joserfc/security/advisories/GHSA-w5r5-m38g-f9f9 x_refsource_CONFIRM
- https://github.com/authlib/joserfc/commit/696a9611ab982c45ee2190ed79ca8e1d8e09398f x_refsource_MISC
- https://nvd.nist.gov/vuln/detail/CVE-2026-27932 advisory
- https://github.com/advisories/GHSA-w5r5-m38g-f9f9 advisory
- https://github.com/authlib/joserfc/commit/696a961 patch
- https://github.com/authlib/joserfc url