Attack Chain

1. Attacker performs reconnaissance to identify internet-facing Microsoft SharePoint instances.
2. If anonymous access is enabled, the attacker chains existing auxiliary vulnerabilities to bypass initial authentication.
3. Attacker targets the specific code injection vector defined by CVE-2026-65660.
4. The malicious request triggers the underlying vulnerability, allowing for code execution within the SharePoint application context.
5. Attacker executes arbitrary commands, potentially deploying a web shell to maintain persistence (e.g., via T1505.003).
6. Attacker leverages the elevated application context to perform further privilege escalation or move laterally within the server environment.
7. Attacker achieves the final objective, which may include data exfiltration or internal network reconnaissance.

Impact

Successful exploitation allows attackers to gain full code execution on affected SharePoint servers. This can lead to total system compromise, unauthorized access to sensitive internal data, and the establishment of persistent backdoors within the organization's network. Given that many SharePoint instances store critical business and enterprise data, the impact of a successful breach is significant. Organizations running EOL versions (2016 and 2019) are at a particularly elevated risk, as they no longer receive standard support and may lack defense-in-depth protections.

Recommendation

Prioritize the immediate upgrade of all SharePoint instances to the fixed versions listed below. Enable Antimalware Scan Interface (AMSI) integration for SharePoint web applications and set the scan mode to 'Full' to improve detection of malicious payloads. Restrict access to management interfaces like SharePoint Central Administration and ensure all internet-facing instances are shielded from unnecessary exposure. Monitor IIS and SharePoint logs for anomalous administrative behavior, unauthorized web part modifications, and unexpected deserialization activity that may signal exploitation.