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CVE-2026-75757 – Session/Actor Hijacking via Cookie Confusion – ash_admin 0.9.1 to before 1.3.1

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Summary

CVE-2026-75757 is a cookie-validation vulnerability (CWE-565: Reliance on Cookies without Validation and Integrity Checking) in ash_admin, the admin UI package for the Ash Framework (Elixir). An attacker who controls a sibling subdomain of an application hosting ash_admin can plant crafted cookies that are silently accepted by the admin interface’s client-side JavaScript, allowing the attacker to rebind an administrator’s session to a different actor, tenant, or authorization mode. The issue carries a CVSS v4.0 base score of 8.3 (High) and affects versions 0.9.1 up to (but not including) 1.3.1.

Technical details

  • Root cause: The cookie-reading logic in the AshAdmin JavaScript bundle builds a regular expression as new RegExp(cookieName + "=([^;]+)") without anchoring the match to the start of the cookie name. As a result, the match succeeds against any cookie whose name merely ends with the requested cookie name rather than matching it exactly.
  • Trigger conditions: The attacker must control a sibling subdomain (or otherwise be able to set cookies scoped to a parent domain shared with the AshAdmin application) so that a maliciously named cookie is sent alongside the legitimate ones.
  • Attack vector: Network-based, no privileges required, no user interaction required beyond visiting/loading the admin page while attacker-set cookies are present (CVSS AV:N/AC:L/AT:P/PR:N/UI:N).
  • Impact: By planting a cookie such as xactor_authorizing=… or evil_actor_paused=…, an attacker can satisfy lookups for legitimate cookie names like actor_authorizing or actor_paused. These attacker-controlled values then flow unvalidated into the LiveSocket connection parameters used by AshAdmin, letting the attacker manipulate the acting actor, tenant context, or authorization mode of an administrator’s session — an integrity impact on session state (CVSS VI:H) without directly exposing confidentiality of other data.

Affected software

  • ash_admin (Elixir/Ash Framework admin UI package): versions >= 0.9.1 and < 1.3.1

Severity

  • CVSS v4.0 Base Score: 8.3 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N
  • CWE: CWE-565 (Reliance on Cookies without Validation and Integrity Checking)

Mitigation and recommended actions

  • Immediate: Upgrade ash_admin to version 1.3.1 or later, which fixes the flaw by comparing cookie names for exact equality (splitting document.cookie on semicolons) instead of using an unanchored substring/regex match.
  • If immediate patching is not possible:
    • Avoid deploying AshAdmin on a domain that shares a parent domain with untrusted or third-party-controlled sibling subdomains.
    • Ensure strict subdomain isolation and cookie scoping (e.g., avoid overly broad Domain= attributes on cookies) so that sibling subdomains cannot set cookies visible to the AshAdmin origin.
    • Restrict access to the AshAdmin interface (e.g., via network-level access controls, VPN, or IP allowlisting) to reduce exposure until the patch can be applied.

References

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