Cloudflare protects against critical SharePoint vulnerability, CVE-2025-53770
Jul 22, 2025Jin-Hee Lee, Vaibhav Singhal
Summary
This post details Cloudflare's rapid response to CVE-2025-53770 and CVE-2025-53771, critical SharePoint vulnerabilities. It explains the ToolShell exploit chain, which involves an authentication bypass via `Referer` header manipulation, a deserialization RCE, and the theft of cryptographic keys for persistent access. Cloudflare's WAF Managed Rules were updated with emergency releases to mitigate these threats, demonstrating a proactive security posture and rapid response to zero-day exploits. The post includes metrics on the number of blocked exploit attempts.
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