Vulnerability Description
Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to impersonate another user via the user parameter of the authorization callback. Apple posts the user's name to the callback endpoint in a user form parameter that the browser submits and the client controls. Assent.Strategy.Apple.callback/2 in lib/assent/strategies/apple.ex decodes that parameter, and fetch_user/2 merges it over the claims of the verified ID token, so the unverified map wins. An attacker who completes a Sign in with Apple login with their own Apple ID and edits the user parameter can replace sub, email, and any other claim. Applications that look up, link, or authorize accounts by the returned subject or email then act on the attacker's values. This issue affects assent: from 0.1.25 before 0.3.2.
Related Weaknesses (CWE)
References
- https://cna.erlef.org/cves/CVE-2026-117656.html
- https://github.com/pow-auth/assent/commit/18898bde0296152165ae470078490e5798329b
- https://github.com/pow-auth/assent/commit/a2d331e8c51376d6c0b04a81aad31e0b4d4d64
- https://github.com/pow-auth/assent/security/advisories/GHSA-9fr5-g44g-9526
- https://osv.dev/vulnerability/EEF-CVE-2026-117656
FAQ
What is CVE-2026-117656?
CVE-2026-117656 is a documented vulnerability. Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to impersonate another user via ...
How severe is CVE-2026-117656?
CVSS scoring is not yet available for CVE-2026-117656. Check NVD for updates.
Is there a patch for CVE-2026-117656?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.