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High, CVSS 7.7amended

Authlib: Setting alg: none and a blank signature appears to bypass signature verification

CVE-2026-28802GHSA-7wc2-qxgw-g8gg

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (authlib 1.6.7), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI authlib

    Affected
    >= 1.6.5, <= 1.6.6
    Fixed in
    1.6.7

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
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 · score source
EPSS
  • CVE-2026-28802: 0.54% estimated exploitation activity in the next 30 days; percentile 45.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary After upgrading the library from 1.5.2 to 1.6.0 (and the latest 1.6.5) it was noticed that 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. Details It was likely introduced in this commit: https://github.com/authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75 PoC Output: Impact Users of the library are likely not aware that they now need to check the provided headers and disallow alg: none usage, it is not obvious from the release notes that any action needs to be taken. As a best-practice, the library should adopt a 'secure by default' stance and default to rejecting it and allow the application to provide an algorithm whitelist. Applications using this library for authentication or authorization may accept malicious, forged JWTs, leading to: - Authentication bypass - Privilege escalation - Unauthorized…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-7wc2-qxgw-g8gg

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-7wc2-qxgw-g8gg

Agent brief

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# Patch Next advisory brief: CVE-2026-28802

Advisory: Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
IDs: CVE-2026-28802, GHSA-7wc2-qxgw-g8gg
Record: https://patchnext.com/advisories/cve-2026-28802 (revision 3, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: authlib 1.6.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI authlib: affected >= 1.6.5, <= 1.6.6; fixed in 1.6.7

## Suggested inspection (read-only)
- `python -m pip show authlib`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on authlib.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-7wc2-qxgw-g8gg (OSV record GHSA-7wc2-qxgw-g8gg lists affected ranges: PyPI authlib >=1.6.5 <1.6.7 (fixed))
- Verified: https://github.com/advisories/GHSA-7wc2-qxgw-g8gg (GitHub-reviewed advisory GHSA-7wc2-qxgw-g8gg lists affected ranges: PyPI authlib >=1.6.5 <=1.6.6)

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