CVE-2026-86688
Session id is not renewed on authentication in ash_authentication, allowing session fixation
- State
- Published
- Severity
- 7.4 High
- Published
- Sep 17, 2026
- Updated
- Sep 18, 2026
- Reserved
- Sep 17, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 7.4 High | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N | EEF |
Weaknesses
- CWE-384 Session Fixation
Affected Products
| Product | Versions |
|---|---|
ash_authenticationteam-alembic |
|
ash_authenticationteam-alembic |
|
References
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