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

> Attackers can cause resource exhaustion by sending oversized unencoded JWS payloads that bypass size limits in the joserfc library.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Jun 2026
- **Updated:** 18 Jun 2026
- **Also known as:** CLEANSTART-2026-QT40101, DEBIAN-CVE-2026-48990, GHSA-wphv-vfrh-23q5, MINI-22v5-7782-8j2c, PYSEC-2026-2530, ROOT-APP-PYPI-CVE-2026-48990, UBUNTU-CVE-2026-48990, openSUSE-SU-2026:11067-1

## What is CVE-2026-48990?

CVE-2026-48990 is a medium-severity denial of service vulnerability in authlib joserfc, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-48990?

3 open source packages ship an affected version, including joserfc.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `joserfc` | PyPI | From 1.3.4 | 1.6.7 |
| `joserfc` | PyPI | From 1.3.4 | 1.6.7 |
| `joserfc` | PyPI | From 1.3.4 | 1.6.7 |
| `python-joserfc` | openSUSE:Tumbleweed | All versions | 1.7.1-1.1 |

## How do I fix CVE-2026-48990?

Upgrade joserfc to 1.6.7 or later.

## Is CVE-2026-48990 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48990 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48990 and fix it if it is affected.

What it is: CVE-2026-48990 is a medium-severity denial of service vulnerability in authlib joserfc, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48990 exists.

Affected packages and fixed versions:
- joserfc (PyPI): affected from 1.3.4; fixed in 1.6.7
- joserfc (PyPI): affected from 1.3.4; fixed in 1.6.7
- joserfc (PyPI): affected from 1.3.4; fixed in 1.6.7

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-48990/ (Markdown: https://insights.sbomify.com/CVE-2026-48990/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48990
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48990
- OSV: https://osv.dev/vulnerability/CVE-2026-48990

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-48990/
Summaries are generated and may contain mistakes; the official description above is the record.