# CVE-2026-48990: authlib joserfc resource exhaustion via oversized RFC7797 payloads

Source: https://junglewise.ai/threats/cve-2026-48990-authlib-joserfc-resource-exhaustion-via-oversized-rfc7797  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-17. Updated: 2026-06-26  
License: CC BY 4.0 with a link back

CVE-2026-48990 · Severity: medium · CVSS 5.3 · Published 2026-06-17

The joserfc library, used for handling secure web tokens (JWS), fails to enforce size limits on certain types of unencoded data. An attacker could send an excessively large token to a server, potentially causing the application to crash or consume all available memory. This can lead to a service outage or significant performance degradation.

Technologies: [Authlib Joserfc](https://junglewise.ai/threats/technologies/joserfc), [joserfc (PyPI)](https://junglewise.ai/threats/technologies/pypi-joserfc). Vendors: [Authlib](https://junglewise.ai/threats/vendors/authlib), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-48990 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-48990 being exploited in the wild.

**How severe is CVE-2026-48990?** Medium severity, with a CVSS score of 5.3, published 17 June 2026.

**Which products and versions are affected?** Authlib Joserfc >= 1.3.4, < 1.6.7, >= 1.3.4, <= 1.6.5; joserfc (PyPI) ECOSYSTEM:introduced=1.3.4,fixed=1.6.7.

**Is there a fix for CVE-2026-48990?** Yes. joserfc (PyPI): upgrade to 1.6.7 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-48990 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-48990?** Check whether you run Authlib Joserfc or joserfc (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- joserfc (PyPI): upgrade to 1.6.7 or later

  ```sh
  pip install "joserfc>=1.6.7"
  ```


## Technical details

A vulnerability in joserfc's deserialization logic allows RFC7797 JWS payloads with the 'b64=false' header to bypass configured size limits. While standard JWS paths correctly invoke validate_payload_size() before decoding, the unencoded payload paths in both compact and flattened JSON deserialization assign the payload segment directly without validation. An unauthenticated remote attacker can exploit this by providing oversized payloads to trigger resource exhaustion or DoS. The issue is fixed in version 1.6.7 by ensuring registry.validate_payload_size() is called for unencoded payload segments.

## Affected products

- authlib joserfc >= 1.3.4, < 1.6.7

## Identifiers

- CVE-2026-48990
- GHSA-wphv-vfrh-23q5
- PYSEC-2026-2530

## Timeline

- 2026-05-24: disclosed
- 2026-06-26: advisory: GitHub Advisory published
- 1.6.7: patched

## References

- [https://api.github.com/users/0xHunSec](https://api.github.com/users/0xHunSec)
- [https://github.com/0xHunSec](https://github.com/0xHunSec)
- [https://api.github.com/users/0xHunSec/gists%7B/gist_id%7D](https://api.github.com/users/0xHunSec/gists%7B/gist_id%7D)
- [https://api.github.com/users/0xHunSec/repos](https://api.github.com/users/0xHunSec/repos)
- [https://avatars.githubusercontent.com/u/39668014?v=4](https://avatars.githubusercontent.com/u/39668014?v=4)
- [https://api.github.com/users/0xHunSec/events%7B/privacy%7D](https://api.github.com/users/0xHunSec/events%7B/privacy%7D)

## Related threats

- [joserfc memory exhaustion in compact JWS deserialization](https://junglewise.ai/threats/cve-2026-119284-joserfc-is-a-python-library-that-provides-an-implementation-of)
- [joserfc JWE denial of service via unlimited recipients](https://junglewise.ai/threats/cve-2026-119283-joserfc-is-a-python-library-that-provides-an-implementation-of)
- [authlib joserfc issuer validation bypass in JWT claims](https://junglewise.ai/threats/cve-2026-75509-authlib-joserfc-issuer-validation-bypass-in-jwt-claims)
- [authlib joserfc token malleability via trailing padding](https://junglewise.ai/threats/cve-2026-62995-authlib-joserfc-token-malleability-via-trailing-padding)
- [authlib joserfc authentication bypass via empty HMAC key](https://junglewise.ai/threats/cve-2026-49852-authlib-joserfc-authentication-bypass-via-empty-hmac-key)