Parallel Intrusion: Storm-2603 and Unattributed Actors Target Microsoft SharePoint
Parallel intrusions were identified in on-premises Microsoft SharePoint environments via the exploitation of CVE-2025-49704, CVE-2025-49706, and CVE-2025-53770. Two distinct threat actors operated concurrently: Storm-2603, a ransomware group utilizing BYOVD and legitimate remote tools, and an unattributed actor focused on Active Directory (AD) credential theft via DLL sideloading and custom backdoors. This overlapping activity created significant "signal noise," complicating forensic detection and containment. The intrusions highlight a critical failure in patching internet-facing legacy infrastructure, enabling both immediate financial extortion and long-term espionage within the same network perimeter.
Critical Hardening Required for Microsoft SharePoint On-Premises Deployments
CISA has added several Microsoft SharePoint on-premises vulnerabilities to the Known Exploited Vulnerabilities (KEV) catalog, signaling active weaponization. The attack surface includes critical RCE via insecure deserialization (CVE-2026-58644, CVSS 9.8) and unauthenticated remote exploitation via CVE-2026-56164. These flaws enable attackers to establish initial footholds, facilitating lateral movement toward Domain Controllers and backup systems for full infrastructure encryption. Remediation requires immediate patching, AMSI integration, and the rotation of SharePoint machine keys to neutralize persistent access.