CVE-2026-27932 joserfc PBES2 p2c Unbounded Iteration Count enables Denial of Service (DoS)
An unauthenticated attacker can cause CPU exhaustion and Denial of Service in joserfc by sending a JWE token with an unbounded PBES2 iteration count.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27932?
CVE-2026-27932 is a high-severity denial of service vulnerability in authlib joserfc, published on 3 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-770
Which versions are affected by CVE-2026-27932?
3 open source packages ship an affected version, including joserfc. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
joserfc PyPI | All versions | 1.6.3 |
joserfc PyPI | All versions | 1.6.3 |
joserfc PyPI | All versions | 1.6.3 |
Linux distribution packages (2)
python-joserfc openSUSE:Leap 16.0 | All versions | 1.1.0-bp160.2.1 |
python-joserfc openSUSE:Tumbleweed | All versions | 1.6.3-1.1 |
Products include Hsiaoming Joserfc.
How do I fix CVE-2026-27932?
Upgrade joserfc to 1.6.3 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-27932 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27932 exists.
Other vulnerabilities in authlib joserfc
Sources
Also known as DEBIAN-CVE-2026-27932, GHSA-w5r5-m38g-f9f9, PYSEC-2026-2529, ROOT-APP-PYPI-CVE-2026-27932, UBUNTU-CVE-2026-27932, openSUSE-SU-2026:10293-1 and 1 more.