EEF-CVE-2026-81637 CVE-2026-81637 GHSA-3vcj-gxx8-3p44

Replayable OAuth2 CSRF state retained after a failed callback in AshAuthentication

Not rated yet Hex

Severity: 0.0 / 10; Unknown · CVSS 4.0
Exploit chance (EPSS): 0.61%; Chance of exploitation in the next 30 days. Higher than 49.06% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-613 Insufficient Session Expiration
Fix: 5.0.0-rc.14; Upgrade ash_authentication to this version or later

Description

Summary

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.

Affected versions

Hex

Package	Vulnerable	Fixed in
ash_authentication	`>= 0.6.0, < 4.15.0` `>= 5.0.0-rc.0, < 5.0.0-rc.14`	`4.15.0` `5.0.0-rc.14`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

ash_authentication Hex → `5.0.0-rc.14`

mix

{:ash_authentication, "~> 5.0.0-rc.14"} # then: mix deps.update ash_authentication

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: High
Attack requirements: Present
Privileges required: None
User interaction: Passive
Confidentiality (vulnerable system): Low
Integrity (vulnerable system): Low
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

Weakness

CWE-613: Insufficient Session Expiration

According to WASC, "Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization."

How to prevent it

Implementation: Set sessions/credentials expiration date.

References

Advisories

github.com/team-alembic/ash_authentication/security/advisories/GHSA-3vcj-gxx8-3p44

Fixes and patches

Packages

hex.pm/packages/ash_authentication

Timeline

Sep 17, 2026 Published
Sep 18, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
EEF-CVE-2026-86688 Session id is not renewed on authentication in ash_authentication, allowing session fixation	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-76949 Remember-me sign-in guard reads a session key that is never written in ash_authentication, allowing session replacement	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-91039 dynamic_oidc identities are not namespaced by connection in ash_authentication, allowing cross-connection account takeover	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-88952 OAuth2 sign-in attached to an existing account without an email comparison in AshAuthentication	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-85500 `require_confirmed_with` is not enforced on the action and fails open on an unreadable attribute in AshAuthentication	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-86533 Revoked session accepted because the session jti is never checked in AshAuthentication and AshAuthentication Phoenix	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-81632 Single-use sign-in token placed in a redirect query string in AshAuthenticationPhoenix	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-80218 Sign-in token minted for one resource accepted by another in AshAuthentication	Not rated yet	Also affects ash_authentication

Credits: James Harton, Jonatan Männchen / EEF, Peter Ullrich

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