CVE-2026-48990 joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization
Attackers can cause resource exhaustion by sending oversized unencoded JWS payloads that bypass size limits in the joserfc library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-48990?
CVE-2026-48990 is a medium-severity denial of service vulnerability in authlib joserfc, published on 17 Jun 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 versions 1.3.4 through 1.6.5, joserfc accepts oversized RFC7797 b64=false JWS payloads without applying JWSRegistry.max_payload_length, which can lead to resource exhaustion. The normal JWS compact and flattened JSON paths reject payloads above the configured payload-size limit with ExceededSizeError. The RFC7797 unencoded payload paths do not make the same check. A valid b64=false compact or flattened JSON JWS can therefore deserialize successfully with a payload larger than JWSRegistry.max_payload_length. Applications that accept lower-trust JWS values and rely on joserfc to reject oversized token content during verification have a moderate availability risk. This issue has been fixed in version 1.6.7.
Which versions are affected by CVE-2026-48990?
3 open source packages ship an affected version, including joserfc.
| Package | Affected | Fixed in |
|---|---|---|
joserfc PyPI | From 1.3.4 | 1.6.7 |
joserfc PyPI | From 1.3.4 | 1.6.7 |
joserfc PyPI | From 1.3.4 | 1.6.7 |
Linux distribution packages (1)
python-joserfc openSUSE:Tumbleweed | All versions | 1.7.1-1.1 |
How do I fix CVE-2026-48990?
Upgrade joserfc to 1.6.7 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-2026-48990 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48990 exists.
Sources
Also known as CLEANSTART-2026-QT40101, DEBIAN-CVE-2026-48990, GHSA-wphv-vfrh-23q5, MINI-22v5-7782-8j2c, PYSEC-2026-2530, ROOT-APP-PYPI-CVE-2026-48990 and 2 more.