# 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.

- **Severity:** High 8.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Aug 2026
- **Updated:** 31 Aug 2026
- **Also known as:** EEF-CVE-2026-75757, GHSA-3259-55fp-w94j

## 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 (Reliance on Cookies without Validation and Integrity Checking)

## Which versions are affected by CVE-2026-75757?

1 open source package ship an affected version, including ash_admin.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-75757 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-75757 exists.

Affected packages and fixed versions:
- ash_admin (Hex): affected from 0.9.1; fixed in 1.3.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-75757/ (Markdown: https://insights.sbomify.com/CVE-2026-75757/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-75757
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-75757
- OSV: https://osv.dev/vulnerability/CVE-2026-75757

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-75757/
Summaries are generated and may contain mistakes; the official description above is the record.