# CVE-2026-66420: MeshCentral Cross-Site WebSocket Hijacking via Origin Validation Bypass on Self-Signed Certificate Deployments

> Attackers can hijack administrator sessions and gain full control of managed devices by bypassing origin validation on self-signed certificate deployments.

- **Severity:** High 8.6 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 30 Jul 2026
- **Updated:** 24 Sep 2026
- **Also known as:** GHSA-fcvp-v754-r7rh

## What is CVE-2026-66420?

CVE-2026-66420 is a high-severity authentication bypass vulnerability in Ylianst MeshCentral, published on 30 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

MeshCentral 1.1.21 contains a cross-site WebSocket hijacking protection bypass vulnerability that allows unauthenticated remote attackers to hijack authenticated administrator sessions by exploiting an unconditional early return in the CheckWebServerOriginName() function within webserver.js when self-signed certificates are in use. Attackers can open cross-origin WebSocket connections to any of the twelve WebSocket endpoints, send crafted action commands to exfiltrate the server sessionKey used to sign session cookies, forge session tokens as arbitrary users, and gain full remote control of all managed devices governed by the MeshCentral instance.

Weakness: CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-66420?


## How do I fix CVE-2026-66420?

No fix has been published for CVE-2026-66420 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-66420 being exploited?

There is no known exploitation of CVE-2026-66420 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66420 and fix it if it is affected.

What it is: CVE-2026-66420 is a high-severity authentication bypass vulnerability in Ylianst MeshCentral, published on 30 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-66420 in the wild and no public exploit code.

Affected product: Ylianst MeshCentral. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-66420/ (Markdown: https://insights.sbomify.com/CVE-2026-66420/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66420
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66420
- OSV: https://osv.dev/vulnerability/CVE-2026-66420

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66420/
Summaries are generated and may contain mistakes; the official description above is the record.