Cloudflare CDN flaw leaks user location data, even through secure chat apps

A researcher found that Cloudflare's CDN caching and a flaw in Cloudflare Workers (and the Teleport tool) can be abused to perform zero-click, coarse-grained geolocation of users by sending images hosted on Cloudflare and enumerating which data centers serve the requests; the technique can localize targets within roughly 50–300 miles and affects apps that auto-download images (like Signal and Discord). Cloudflare patched the Workers abuse, awarded a bounty, and noted users can disable caching, but the researcher demonstrated a VPN-based workaround that still reaches many datacenters and enables the attack in many populated regions.