# CVE-2026-28802: Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

> Attackers can bypass JWT signature verification by using the 'none' algorithm, allowing unauthorized access in applications using Authlib.

- **Severity:** High 7.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Mar 2026
- **Updated:** 10 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-28802, ECHO-579f-8639-173e, GHSA-7wc2-qxgw-g8gg, MINI-7crv-x7r7-4m48, MINI-8674-jf8j-vqq2, PYSEC-2026-2118, ROOT-APP-PYPI-CVE-2026-28802, UBUNTU-CVE-2026-28802

## What is CVE-2026-28802?

CVE-2026-28802 is a high-severity authentication bypass vulnerability in authlib, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-28802?

3 open source packages ship an affected version, including authlib. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `authlib` | PyPI | From 1.6.5 | 1.6.7 |
| `authlib` | PyPI | From 1.6.5 | 1.6.7 |
| `authlib` | PyPI | From 1.6.5 | 1.6.7 |

Products: Authlib Authlib.

## How do I fix CVE-2026-28802?

Upgrade authlib to 1.6.7 or later.

## Is CVE-2026-28802 being exploited?

There is no known exploitation of CVE-2026-28802 in the wild and no public exploit code.

## Other vulnerabilities in authlib

- [CVE-2026-27962](https://insights.sbomify.com/CVE-2026-27962/): Authlib JWS JWK Header Injection: Signature Verification Bypass (critical 9.1)
- [CVE-2026-28490](https://insights.sbomify.com/CVE-2026-28490/): Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle (high 8.3)
- [CVE-2026-28498](https://insights.sbomify.com/CVE-2026-28498/): Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding (high 8.2)
- [CVE-2025-61920](https://insights.sbomify.com/CVE-2025-61920/): Authlib is vulnerable to Denial of Service via Oversized JOSE Segments (high 7.5)
- [CVE-2025-59420](https://insights.sbomify.com/CVE-2025-59420/): Authlib: JWS/JWT accepts unknown crit headers (RFC violation → possible authz bypass) (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28802 and fix it if it is affected.

What it is: CVE-2026-28802 is a high-severity authentication bypass vulnerability in authlib, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-28802 in the wild and no public exploit code.

Affected packages and fixed versions:
- authlib (PyPI): affected from 1.6.5; fixed in 1.6.7
- authlib (PyPI): affected from 1.6.5; fixed in 1.6.7
- authlib (PyPI): affected from 1.6.5; 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-2026-28802/ (Markdown: https://insights.sbomify.com/CVE-2026-28802/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28802
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28802
- OSV: https://osv.dev/vulnerability/CVE-2026-28802

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28802/
Summaries are generated and may contain mistakes; the official description above is the record.