CVE Catalog

CVE-2026-117656

CriticalCVSS 9.3
Published: Translated: NVD NIST

Summary

The pow-auth Assent library's Sign in with Apple strategy trusts the browser-supplied 'user' parameter, which the client controls. That parameter is merged over the verified ID token claims, allowing an unauthenticated remote attacker to impersonate another user. Affects versions from 0.1.25 before 0.3.2.

Risk Assessment

An attacker can impersonate a victim (sub, email) and gain access to their account in applications that look up, link, or authorize users by the returned data. This leads to account takeover and access control bypass.

Recommendation

Update the assent library to version 0.3.2 or later. Until patched, do not trust the 'user' callback parameter and verify identity solely from the signed ID token.

Related vulnerabilities

Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS