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HighVulnerabilityCVE-2026-116672updated 30 Oct 2026, 23:09 UTC

Authlib client registration endpoint lets one client change another client's settings

A client holding its own valid access token could read, change, or delete a different client's registration. Changing redirect addresses could let an attacker steal login codes or tokens.

Fixed in Authlib 1.9.1 · out Official, 2 sources
SeverityHighCVSS 8.8 of 10
Being exploited?UnclearNo reports either way yet
Fix available?YesAuthlib 1.9.1 · since 30 Oct 2026
How sure is this?Official, 2 sourcesBacked by an official source

How the attack works simplified

  1. 1Attacker holds tokenAny valid registration access token for their own client
  2. 2Sends requestSupplies another client's client_id in the payload
  3. 3Missing ownership checkEndpoint never verifies the token matches the target client
  4. 4Registration changedRedirect URIs altered or client deleted
  5. ResultOther clients' registrations are hijacked or removed

What happened

In Authlib's RFC 7592 ClientConfigurationEndpoint, the documented example implementations of authenticate_client and check_permission never check that the presented registration access token belongs to the target client identified by client_id, allowing any valid token to act on any client's registration.

Why it is dangerous: An attacker with any valid registration access token can modify redirect_uris to intercept authorization codes or tokens, or delete other clients' registrations causing denial of service. Deployments that copied the documented examples are at risk.

Are you affected?

You are affected if you run Authlib from 0.15 through 1.9.0 and implement the ClientConfigurationEndpoint methods following the documented examples (client lookup by request client_id and checking only client.editable).

Package / productAffected versionsFixed in
Authlib · pip>= 0.15, <= 1.9.01.9.1

What to do

  1. Update Authlib to version 1.9.1 or later
  2. If you cannot update yet, make authenticate_client and check_permission verify that request.credential belongs to the target client
  3. Review existing client registrations for unexpected redirect_uris changes

Timeline

  1. 27 Oct 2026, 17:16 UTC
    Publicly disclosed
  2. 27 Oct 2026, 17:16 UTC
    Reported by NVD · NVD
  3. 27 Oct 2026, 17:20 UTC
    Picked up by Zero Radar
  4. 30 Oct 2026, 23:09 UTC
    GitHub Advisory reported on it · GitHub Advisory
  5. 30 Oct 2026, 23:09 UTC
    Fixed version published: Authlib 1.9.1 · GitHub Advisory

Sources 2 reports, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
CVE-2026-116672 · GHSA-c73q-w75p-j82v
CVSS
8.8 / 10
EPSS
0.3% chance of exploitation within 30 days
Disclosed
27 Oct 2026, 17:16 UTC
On Zero Radar
27 Oct 2026, 17:20 UTC (4 min after disclosure)
Last change
30 Oct 2026, 23:09 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

Authlib client registration endpoint lets one client change another client's settings · Zero Radar