CVE-2026-86688 - Session id is not renewed on authentication in ash_authentication, allowing session fixation

CVE-2026-86688 - Session id is not renewed on authentication in ash_authentication, allowing session fixation

https://cvefeed.io/rssfeed/latest.atom / Fri, 09/18/2026 - 01:32
CVE ID :CVE-2026-86688
Published : Sept. 17, 2026, 10:17 p.m. | 51 minutes ago
Description :Session Fixation vulnerability in team-alembic ash_authentication allows an attacker who can plant a session identifier in a victim's browser to hold an authenticated session once that victim signs in. AshAuthentication.Plug.Helpers.store_in_session/2 writes the authenticated subject into the existing session with Plug.Conn.put_session/3 and never calls Plug.Conn.configure_session(renew: true), so the identifier the visitor arrived with carries into their authenticated session. Every authentication event reaches this one function: the default success/4 injected by AshAuthentication.Phoenix.Controller.__using__/1, the AuthController emitted by mix ash_authentication_phoenix.install, and remember-me auto-login. AshAuthentication.Phoenix.Plug.store_in_session/2 is a defdelegate to it. Logout does not close the window either, because clear_session/2 ends with Plug.Conn.clear_session/1, which clears session contents but leaves the identifier intact, so a planted identifier survives a logout-then-login cycle. This issue affects ash_authentication: from 0.2.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.
Severity: 7.4 | HIGH
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