# CVE-2026-66420 — Ylianst MeshCentral

> As of 2026-07-31, CVE-2026-66420 is a HIGH-severity vulnerability in Ylianst MeshCentral, CVSS v3.1 8.8, EPSS 0.1% (6.1th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-66420 as of 2026-07-31; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-07-31

## What is CVE-2026-66420?

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.

The record classifies CVE-2026-66420 under weakness class [CWE-346](https://intel.threadlinqs.com/cwe/CWE-346). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 67 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 8.8 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **CVSS v4.0 base score:** 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`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 6.1% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-30, last modified 2026-07-31

## Is CVE-2026-66420 being exploited?

It currently carries a trending score of 31 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **Ylianst**: MeshCentral

## How to fix CVE-2026-66420

No vendor patch reference has been recorded for CVE-2026-66420 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-66420

No threat campaign in the Threadlinqs corpus currently references CVE-2026-66420, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-08-02. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com — product](https://github.com/Ylianst/MeshCentral/pull/7882)
- [github.com — patch](https://github.com/Ylianst/MeshCentral/commit/f04c9f4)

**Third-party advisory**

- [vulncheck.com — third party advisory](https://www.vulncheck.com/advisories/meshcentral-cross-site-websocket-hijacking-via-origin-validation-bypass-on-self-signed-certificate-deployments)

**Issue tracking and product pages**

- [github.com — product](https://github.com/Ylianst/MeshCentral)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-66420
Full detection coverage and IOCs for threats exploiting CVE-2026-66420 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp