OAuthLib: Token grants can use attacker-supplied client_id for authorization after authenticating a different client

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:N · score source

EPSS

• CVE-2026-118669: 0.31% estimated exploitation activity in the next 30 days; percentile 24.19 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary OAuthlib's token grant handlers can authenticate one client while authorizing the grant type and requested scopes using a different, attacker-supplied `client_id` from the request body. In affected token grant flows, `authenticate_client(request)` sets `request.client` to the authenticated client object, but OAuthlib does not require `request.client_id` to match `request.client.client_id`. If the request body already contains `client_id=...`, OAuthlib keeps that value and passes it to `validate_grant_type()` and `validate_scopes()`. As a result, an authenticated low-privilege confidential client can authenticate as itself, submit another client's `client_id` in the token request body, and cause grant and scope validation to run under that other client identity.

Affected Surface The affected public surface is the OAuth2 token endpoint handling for: - `client_credentials` - `password` / Resource Owner Password Credentials The issue is relevant to OAuthlib provider…

Published by the source

30 Oct 2026, 22:58 UTC

Last modified by the source

30 Oct 2026, 23:15 UTC

Source last checked

31 Oct 2026, 06:15 UTC

1. Revision 2 · amended · 31 Oct 2026

   Amended from osv record GHSA-7984-qgvg-3j9c

2. Revision 1 · created · 30 Oct 2026

   Published from ghsa record GHSA-7984-qgvg-3j9c

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# Patch Next advisory brief: CVE-2026-118669

Advisory: OAuthLib: Token grants can use attacker-supplied client_id for authorization after authenticating a different client
IDs: CVE-2026-118669, GHSA-7984-qgvg-3j9c
Record: https://patchnext.com/advisories/cve-2026-118669 (revision 2, source checked 31 Oct 2026, 06:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: oauthlib 4.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI oauthlib: affected < 4.0.0; fixed in 4.0.0

## Suggested inspection (read-only)
- `python -m pip show oauthlib`: 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 oauthlib.
- 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://github.com/advisories/GHSA-7984-qgvg-3j9c (GitHub-reviewed advisory GHSA-7984-qgvg-3j9c lists affected ranges: PyPI oauthlib >=0 <4.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-7984-qgvg-3j9c (OSV record GHSA-7984-qgvg-3j9c lists affected ranges: PyPI oauthlib >=0 <4.0.0 (fixed))

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