CVE-2026-48990: joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization

Vulnerability summary

CVE-2026-48990 is a medium (CVSS 5.3) Uncontrolled Resource Consumption vulnerability in authlib joserfc. EPSS estimates a 0.16% chance of exploitation in the next 30 days, higher than 5.5% of scored vulnerabilities.

Timeline

1. 17-06-2026
   PublishedVulnerability first disclosed.
2. 18-06-2026
   Last modifiedVulnerability information updated.

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.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-770Allocation of Resources Without Limits or ThrottlingThe product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.