Extraction of Pages build scripts, config values, tokens, etc. via symlinks

Summary

Due to a broader permission set on certain folders within the filesystem structure, a malicious Pages build could leverage symlinks to extract build source/configuration and environment variables. While these variables were scoped to allow access to the user's own Pages site data and not the data of others, Cloudflare's Engineering team chose to remediate the issue by tightening permissions on the file system.