CVE-2026-86688

published 2026-09-17

CVE-2026-86688: 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…

Priority P3 46 high 7.4 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 E X CR X IR X AR X MAV X MAC X MAT X MPR X MUI X MVC X MVI X MVA X MSC X MSI X MSA X S X AU X R X V X RE X U X

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.

Affected

3 ranges

Vendor	Product	Version range	Fixed in
team-alembic	ash_authentication	>= 0.2.0 < 4.15.0	4.15.0
team-alembic	ash_authentication	>= 5.0.0-rc.0 < 5.0.0-rc.14	5.0.0-rc.14
team-alembic	ash_authentication	>= a939dde9b917c072cdf10c4b0913a9886a4b0231 < *	*

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CWE-384