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

Affected: authlib joserfc

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.

GHSA-wphv-vfrh-23q5 — joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization

Affected: PyPI: joserfc

# RFC7797 b64=false JWS payloads bypass JWSRegistry payload-size limits during deserialization

## Summary

Testing revealed that `joserfc` accepts oversized RFC7797 `b64=false` JWS payloads without applying `JWSRegistry.max_payload_length`.

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`.

This creates a moderate availability/resource-exhaustion risk for applications that accept lower-trust JWS values and rely on `joserfc` to reject oversized token content during verification.

## Affected Product

- Package: `joserfc` - Ecosystem: `pip` - Audited release: `1.6.5` - Audit tag: `1.6.5` - Audit commit: `881712980934fb601bed26fe3ae1ec0b7780e6f7` - Tested affected releases: `1.3.4`, `1.3.5`, `1.4.2`, `1.6.2`, `1.6.3`, `1.6.4`, `1.6.5` - Fixed release: none known

## Vulnerability Details

In `joserfc` 1.6.5, the default JWS registry has `max_payload_length = 128000` and exposes `validate_payload_size()`.

The normal compact extraction path calls that check before base64url-decoding the payload. The RFC7797 compact path validates the header and signature segment sizes, then assigns the unencoded payload directly:

```text if is_rfc7797_enabled(protected): if not payload_segment and pa…

PYSEC-2026-2530 — joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization