CVE-2026-81637

01/Description

Insufficient Session Expiration vulnerability in team-alembic AshAuthentication allows an attacker who obtains a victim's OAuth2 state value to replay the callback and sign that victim into an attacker-controlled account. AshAuthentication.Strategy.OAuth2.Plug.callback/2 clears the stored session_params through a rebinding step inside its with chain, conn <- delete_session(conn, session_key). Elixir evaluates the else block in the scope enclosing the with, so every failure path (the provider returning ?error=access_denied, an invalid code, a token-exchange error, or a registration or sign-in failure) reaches store_authentication_result/2 holding the original connection and the session entry is never removed. The value the module's own comment describes as protection against a CSRF-related attack is therefore consumed only when authentication succeeds, and survives a cancelled or failed attempt until the next request phase or session expiry. This issue affects ash_authentication: from 0.6.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.

02/References6

• cna.erlef.org/cves/CVE-2026-81637.html
• github.com/team-alembic/ash_authentication/commit/bd4352303bc9d…
• github.com/team-alembic/ash_authentication/commit/c5f589058e042…
• github.com/team-alembic/ash_authentication/commit/d7f939cd02bd6…
• github.com/team-alembic/ash_authentication/security/advisories/…
• osv.dev/vulnerability/EEF-CVE-2026-81637