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9.1

ash_authentication allows attacker to hijack user session via remember-me cookie

CVE-2026-76949 · published 24 days ago
Summary

Versions of ash_authentication from 4.10.0 up to but not including 4.15.0, and from 5.0.0-rc.0 up to 5.0.0-rc.14, may accept a forged remember-me cookie and replace a logged‑in user's session with the attacker’s account. This means an attacker who can place such a cookie in a victim’s browser can control the victim’s actions on the site. Update to the patched versions or disable the remember‑me feature until the update is applied.

What to do
  • Update team-alembic ash_authentication to version 9a34136b844abe179da1075067cf2835c64dcc12.
  • Update ash-project ash_authentication to version 5.0.0-rc.14.
  • Update ash_authentication to version 5.0.0-rc.14.
Affected software
Ecosystem VendorProductAffected versions
– team-alembic ash_authentication < 4.15.0
< *
Fix: upgrade to 9a34136b844abe179da1075067cf2835c64dcc12
Hex ash-project ash_authentication >= 5.0.0-rc.0, < 5.0.0-rc.14
Fix: upgrade to 5.0.0-rc.14
Hex – ash_authentication >= 5.0.0-rc.0, < 5.0.0-rc.14
Fix: upgrade to 5.0.0-rc.14
Original advisory text
Remember-me sign-in guard reads a session key that is never written in ash_authentication, allowing session replacement
Authentication Bypass by Spoofing vulnerability in team-alembic ash_authentication allows an attacker who can plant a remember-me cookie in a victim's browser to replace that victim's authenticated session with one for the attacker's own account.

AshAuthentication.Plug.Helpers.sign_in_using_remember_me/3 skips re-authenticating an already-signed-in visitor by checking the session for "<subject_name>_token", but store_in_session/2 writes that key only when require_token_presence_for_authentication? is enabled and otherwise writes the bare subject name. At the default setting the guard therefore reads a key that is never written, its already-signed-in branch is unreachable, and the remember-me sign-in runs on every request through the per-request browser pipeline plug. A planted remember-me cookie is consequently honoured even for a visitor holding a live authenticated session, so whatever the victim enters afterwards lands in data the attacker controls. The read path in authenticate_resource_from_session/4 selects the key correctly, so the guard and the reader disagree about which key holds the session.

This issue affects ash_authentication: from 4.10.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.
References
Fix within
Internet-facing 3 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically
  • Gives an attacker full control
Severity
9.1 Critical
Exploitation
<1% chance of attack within 30 days
Type
CWE-290Authentication Bypass by Spoofing
Timeline
Published17 Sep 2026
Updated11 Oct 2026
First seen17 Sep 2026
Sources
CVE-2026-76949 · NVD
CVE-2026-76949 · MITRE
EEF-CVE-2026-76949 · OSV
GHSA-hh34-374j-pfr5 · GHSA
CVE-2026-76949 · OSV
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