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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-48990: 0.16% estimated exploitation activity in the next 30 days; percentile 5.50 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.maxpayloadlength. 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.maxpayloadlength. 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:…

Published by the source

26 Jun 2026, 20:59 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wphv-vfrh-23q5

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wphv-vfrh-23q5

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# Patch Next advisory brief: CVE-2026-48990

Advisory: joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization
IDs: CVE-2026-48990, GHSA-wphv-vfrh-23q5
Record: https://patchnext.com/advisories/cve-2026-48990 (revision 2, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: joserfc 1.6.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI joserfc: affected >= 1.3.4, < 1.6.7; fixed in 1.6.7

## Suggested inspection (read-only)
- `python -m pip show joserfc`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on joserfc.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wphv-vfrh-23q5 (OSV record GHSA-wphv-vfrh-23q5 lists affected ranges: PyPI joserfc >=1.3.4 <1.6.7 (fixed))
- Verified: https://github.com/advisories/GHSA-wphv-vfrh-23q5 (GitHub-reviewed advisory GHSA-wphv-vfrh-23q5 lists affected ranges: PyPI joserfc >=1.3.4 <1.6.7)

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