A placeholder domain from W3C specs and MCP docs is serving ClickFix PowerShell lures

Nothing in this chain is fetched by the browser. The page copies a PowerShell command into the Windows clipboard, then instructs the visitor to press Windows key + R, paste with Ctrl+V and press Enter ^[6]. The command runs in the user's own session. That is the property ClickFix is built on: the malware is installed by commands the victim types, not downloaded from a site or opened from an attachment, and BleepingComputer notes this can in some cases get it installed while bypassing traditional antivirus ^[8].

The page also decides who sees the payload. Manifold Security's Ax Sharma says the attack targets Windows users specifically, and that macOS and Linux visitors get an error saying their operating system is unsupported ^[12]. "The attacker only shows the weapon to the targets it works against, which is precisely why a casual look, or a scanner on a Linux datacenter IP, sees nothing wrong," Sharma said ^[13].

The string itself has been in public specifications for years. The W3C Geolocation specification uses third-party.com as the placeholder when demonstrating how to grant geolocation permission to an external iframe ^[15]. The W3C Compute Pressure specification carries the snippet `<iframe src="https://third-party.com" allow="compute-pressure"/>` ^[16]. Chromium's Telemetry Extension API documentation uses it as an example site permitted to talk to a Chrome extension ^[17]. A PrivacyCG proposal on GitHub uses it as the destination of a `fetch()` call from a service worker ^[18]. BleepingComputer names those four and does not put a number on how many documents use the domain ^[4]; Manifold found it while reading public AI skills and MCP server documentation that referenced it ^[4].

Some of those examples reach the network if copied literally ^[19], and posts online indicate developers have copied examples like them into their own code ^[21]. The Compute Pressure iframe is the sharpest case: pasted as written, it loads content controlled by whoever holds the registration, inside the developer's page, with compute-pressure permission granted ^[2]. This is not theoretical. In a 2015 Stack Overflow question, a developer said they had applied an asynchronous loading example containing https://third-party.com/resource.js to their site, and only found out after publishing that it did not behave as expected ^[20].

One domain covers both exposures. A resolver block on third-party.com kills the lure page and any copied code still pointing at it ^[3]. Finding the copies is a search for the literal string across repositories, vendored dependencies and skill files.