The Rising Threat of ToolShell: Unpacking the July 2025 SharePoint Zero-Day Exploits
Anatomy of the ToolShell Exploit Chain Beginning around July 7, 2025, adversaries exploited a deserialization flaw in SharePoint’s on-premises service (CVE-2025-53770) to upload a malicious spinstall0.aspx payload, triggering code execution within the w3wp.exe process. A secondary path-traversal flaw (CVE-2025-53771) then enabled privilege escalation and lateral movement across corporate networks . Security researchers at Eye Security and Palo Alto Networks’ Unit 42 observed attackers bypassing identity controls – MFA and SSO – to exfiltrate machine keys, deploy persistent backdoors, and chain ransomware operations within hours of initial compromise . State-Backed Actor Involvement Microsoft attributes the campaign primarily to Storm-2603, assessed with moderate confidence to be China-based, alongside historically linked groups Linen Typhoon and Violet Typhoon . These actors have a track record of blending cyber-espionage with financially motivated ransomware like Warlock and Lo...
