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CVE-2026-85500 – Authentication Bypass – Ash Authentication (ash_authentication) 4.3.8–4.14.x and 5.

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Summary

CVE-2026-85500 is an authentication bypass vulnerability (CWE-287, CWE-754) in Ash Authentication (the ash_authentication Elixir library maintained by team-alembic), rated CRITICAL (CVSS v4.0: 9.1). The flaw allows an attacker to register or sign in and obtain a valid authenticated session while completely bypassing the mandatory email confirmation control, meaning accounts can be created and used with emails the attacker does not own or verify.

Technical details

  • Root cause (fail-open validation): The confirmation check in AshAuthentication.Strategy.Password.Actions.check_user/2 determines whether a user is confirmed using a bare is_nil(Map.get(user, value)) comparison against the attribute named by require_confirmed_with. When that attribute is not selected on the loaded record, Map.get/2 returns %Ash.NotLoaded{}; when a field policy denies access to it, it returns %Ash.ForbiddenField{}. Neither struct equals nil, so the check silently treats these users as already confirmed.
  • Root cause (missing enforcement at the action layer): Confirmation checks are only implemented in wrapper functions inside AshAuthentication.Strategy.Password.Actions, not on the underlying sign_in_with_token and register_with_password actions themselves. Callers that invoke these actions directly — including integrations such as AshGraphql and AshJsonApi — skip the confirmation check entirely.
  • Trigger conditions: Applications that configure require_confirmed_with for email/account confirmation, and either (a) do not force-select the confirmation attribute (leaving it unloaded), (b) apply a field policy that hides the confirmation attribute from the acting user, or (c) expose the affected password actions directly through a GraphQL/JSON:API layer rather than only through the built-in wrapper functions/LiveView forms.
  • Attack vector: Network — no authentication or special privileges are required; public self-registration endpoints are typically sufficient to exploit the flaw.
  • Impact: An unauthenticated attacker can register or authenticate using an unverified or spoofed email address and obtain a fully authenticated session, defeating the application’s email-verification security control. This can enable account takeover, impersonation, or unauthorized access to functionality gated behind "confirmed user" status.

Affected software

  • ash_authentication (Elixir/Ash Framework), maintained by team-alembic:
    • >= 4.3.8, <= 4.14.2 (all versions prior to 4.15.0)
    • >= 5.0.0-rc.0, <= 5.0.0-rc.13 (release-candidate track prior to 5.0.0-rc.14)

Severity

  • CVSS v4.0 Base Score: 9.1 (Critical) — Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
  • Note: The vendor’s GitHub Security Advisory separately scores the same issue as CVSS v3.1: 6.5 (Medium) — Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N. Both scores are published by authoritative sources; the CVE record itself carries the CVSS v4.0 9.1 rating. Security teams should treat this as high-priority given the network-reachable, no-privilege-required nature of the flaw.

Mitigation and recommended actions

  • Immediate: Upgrade ash_authentication to 4.15.0 or later (or 5.0.0-rc.14 or later if on the 5.0 release-candidate track). These releases fix both the fail-open nil comparison and enforce confirmation checks at the action layer.
  • If immediate patching is not possible, apply these workarounds:
    • Do not expose sign_in_with_token or register_with_password actions directly through API layers (e.g., AshGraphql, AshJsonApi) without adding independent, explicit confirmation checks.
    • Ensure the confirmation attribute referenced by require_confirmed_with is always selected by default and is never excluded via select narrowing.
    • Review and remove any field policies that could hide the confirmation attribute from the acting user/actor context.
    • Test sign-in and registration behavior across all exposed routes and API surfaces, not only through default LiveView/UI forms, to confirm unconfirmed users cannot obtain sessions.

References

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