Vulnerability · Published Jun 17, 2026 · Assigned by GitHub_M
CVE-2026-48990joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization
Medium 5.3
In plain English
A medium-severity uncontrolled resource consumption in joserfc from authlib. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | joserfc | no fix listed | DEBIAN-CVE-2026-48990 |
| Debian:14 | joserfc | 1.6.8-1 | DEBIAN-CVE-2026-48990 |
| PyPI | joserfc | 1.6.7 | GHSA-wphv-vfrh-23q5 |
| PyPI | joserfc | 1.6.7 | PYSEC-2026-2530 |
| Ubuntu:25.10 | joserfc | no fix listed | UBUNTU-CVE-2026-48990 |
| Ubuntu:26.04:LTS | joserfc | no fix listed | UBUNTU-CVE-2026-48990 |
Affected products (as reported)
Weakness: CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/authlib/joserfc/security/advisories/GHSA-wphv-vfrh-23q5 x_refsource_CONFIRM
- https://github.com/authlib/joserfc/releases/tag/1.6.7 x_refsource_MISC