What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-17 · updated 2026-10-26
• Weakness: CWE-400

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 products

• authlib joserfc: before 1.6.7

References

• https://github.com/authlib/joserfc/releases/tag/1.6.7
• https://github.com/authlib/joserfc/security/advisories/GHSA-wphv-vfrh-23q5
• https://github.com/authlib/joserfc/security/advisories/GHSA-wphv-vfrh-23q5

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