CVE-2026-27932
HIGHjoserfc PBES2 p2c Unbounded Iteration Count enables Denial of Service (DoS)
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
joserfcReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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 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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | joserfc | all versions | 1.6.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for joserfc. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update joserfc to 1.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27932 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-27932 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-27932. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-27932 in your dependencies?
O3 detects CVE-2026-27932 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.