# CVE-2026-62995: joserfc accepts JWT with padding, leading to JWT malleability

> Attackers can bypass token revocation or anti-replay protections by exploiting JWT malleability caused by non-standard padding acceptance in the joserfc library.

- **Severity:** Low 2.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jul 2026
- **Updated:** 30 Jul 2026
- **Also known as:** CLEANSTART-2026-TT52719, DEBIAN-CVE-2026-62995, GHSA-5jhw-7jv7-qcqq, UBUNTU-CVE-2026-62995, openSUSE-SU-2026:11423-1, openSUSE-SU-2026:21515-1

## What is CVE-2026-62995?

CVE-2026-62995 is a low-severity vulnerability in authlib joserfc, published on 29 Jul 2026. Any signed-in user can exploit it over the network, 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 1.7.1 and prior,  joserfc accepts JWTs with trailing padding (==) which are not conforming to the JOSE specifications. This leads to malleability of the JWTs when consumed by joserfc. Depending on this application this might or not be an issue. This could lead to bypass of token revocation or anti-replay protection when implemented as a deny list of tokens or a deny list of token hashes. Note that ECDSA JWS are always malleable because of the malleability of ECDSA signatures (first test case in the code bellow). This makes a scheme which assumes that JWTs are not malleable brittle. However for other signatures (or MAC) schemes it might make sense to assume non malleability of the token. This issue has been fixed in version 1.7.2.

Weakness: CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2026-62995?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `python-joserfc` | openSUSE:Leap 16.0 | All versions | 1.1.0-bp160.4.1 |
| `python-joserfc` | openSUSE:Tumbleweed | All versions | 1.7.4-2.1 |

## How do I fix CVE-2026-62995?

Upgrade to a fixed version.

## Is CVE-2026-62995 being exploited?

There is no known exploitation of CVE-2026-62995 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-62995 and fix it if it is affected.

What it is: CVE-2026-62995 is a low-severity vulnerability in authlib joserfc, published on 29 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-62995 in the wild and no public exploit code.

Affected product: authlib joserfc. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-62995/ (Markdown: https://insights.sbomify.com/CVE-2026-62995/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-62995
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-62995
- OSV: https://osv.dev/vulnerability/CVE-2026-62995

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-62995/
Summaries are generated and may contain mistakes; the official description above is the record.