CVE-2026-75757 AshAdmin cookie reader matches names by substring, enabling actor/session shadowing from a sibling subdomain
Attackers on sibling subdomains can shadow admin session cookies via substring matching, allowing unauthorized actor or tenant rebinding in AshAdmin.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-75757?
CVE-2026-75757 is a high-severity vulnerability in ash-project ash_admin, published on 31 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Reliance on Cookies without Validation and Integrity Checking vulnerability in ash-project ash_admin lets an attacker who controls a sibling subdomain rebind an admin's session to a different actor, tenant, or authorization mode.
AshAdmin's client JavaScript read its state cookies (tenant, actor_resource, actor_primary_key, actor_action, actor_domain, actor_authorizing, actor_paused) by matching the cookie name with an unanchored regular expression (new RegExp(name + "=([^;]+)")) against the whole document.cookie. Any cookie whose name merely ends with the requested name therefore matches, and whichever is serialized first wins. Because cookies are shared across a registrable domain, a compromised sibling subdomain can set a shadowing cookie (for example xactor_authorizing) with Domain=.example.com that flows unvalidated into the admin's LiveSocket connect params. The fix matches cookie names by exact equality.
This issue affects ash_admin: from 0.9.1 before 1.3.1.
Weakness: CWE-565
Which versions are affected by CVE-2026-75757?
1 open source package ship an affected version, including ash_admin.
| Package | Affected | Fixed in |
|---|---|---|
ash_admin Hex | From 0.9.1 | 1.3.1 |
How do I fix CVE-2026-75757?
Upgrade ash_admin to 1.3.1 or later.
Is CVE-2026-75757 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-75757 exists.
Sources
Also known as EEF-CVE-2026-75757, GHSA-3259-55fp-w94j.