CVE Alert: CVE-2025-53770 – Microsoft – Microsoft SharePoint Enterprise Server 2016

Risk verdict: Critical, actively exploited in the wild; treat as priority 1 due to known exploitation and high-impact RCE.

Why this matters: An unauthenticated network exploit can seize control of on-prem SharePoint servers, enabling full code execution, data exfiltration, and potential further compromise of connected systems. The impact is heightened for organisations with internet-facing or poorly segmented SharePoint deployments, increasing the likelihood of broad impact and ransomware risk.

Most likely attack path: The vulnerability permits remote, low-complexity exploitation with no user interaction and no privileges required, allowing immediate code execution on the target server. Initial access is external-facing; once running, attacker control enables lateral movement within the host and potential pivot to adjacent assets in the network, especially if domain trust and segmentation are weak.

Who is most exposed: Organisations operating on-prem SharePoint Server 2016/2019 or Subscription Edition with exposed web interfaces, common in large enterprises, government, and professional services where intranet/document-sharing portals are Internet-accessible or poorly isolated.

Detection ideas:

• Web server logs show unexpected deserialization-related activity or payloads targeting SharePoint endpoints.
• IIS or application logs indicate suspicious deserialization errors or anomalous gadget chains.
• Sudden spikes in CPU/network on the SharePoint server, or unusual outbound connections from the host.
• SIEM alerts for known IOCs or patterns associated with CVE-2025-53770 exploitation.
• WAF or proxy alerts triggered by automated exploitation attempts.

Mitigation and prioritisation:

• Apply the official patch as soon as released; treat as priority 1 per KEV/SSVC indicators.
• Implement mitigations described by Microsoft interim guidance; disable or tightly filter exposed endpoints.
• Enforce network segmentation and restrict inbound access to SharePoint servers; consider VPN-only access for admin tasks.
• Enhance monitoring with targeted detections for deserialization activity and IIS process anomalies.
• Plan rapid change management: test patch in staging, schedule emergency window, and verify remediation before broad rollout.