Summary Points
- An unauthenticated attacker can exploit CVE-2026-63520 by uploading a malicious Business Data Connectivity (BDC) model, enabling remote code execution (RCE) on SharePoint servers.
- The vulnerability allows arbitrary .NET type instantiation, facilitating gadget chains that trigger Process.Start() with malicious parameters, such as executing system commands like notepad.exe.
- Attackers can bypass authentication (via CVE-2026-55040), gaining full control over SharePoint’s server environment, potentially leading to system compromise, data theft, or further malware deployment.
Threat, Attack Techniques, and Targets
The CVE-2026-63520 vulnerability impacts Microsoft SharePoint, specifically affecting the Business Data Connectivity (BDC) subsystem. An attacker with authenticated access can exploit this flaw to achieve remote code execution (RCE). They do this by uploading a malicious BDC model file and triggering the type instantiation process. The attack leverages the unchecked resolution of .NET types through the Type.GetType() function, which resolves arbitrary assembly-qualified type names without restrictions. This allows the attacker to instantiate any .NET type present in the Global Assembly Cache, including dangerous ones like System.Diagnostics.Process. Attackers can then set properties on these types to execute arbitrary commands or processes on the server. The primary targets are SharePoint servers running vulnerable versions, especially those with exposed BDC models and web services accessible to authenticated users. Notably, the chain of exploitation involves combining the RCE vulnerability with an authentication bypass, making it feasible to conduct attacks without prior unauthenticated access.
Impact, Security Implications, and Remediation Guidance
The exploitation of CVE-2026-63520 can lead to severe consequences. Attackers may gain control over the affected SharePoint server, execute arbitrary commands, or deploy malicious payloads. This can compromise data confidentiality, integrity, and availability. Additionally, the vulnerability’s ability to allow remote code execution can facilitate further attacks such as privilege escalation or lateral movement within a network. Due to the critical nature of this flaw, organizations should seek remediation guidance directly from Microsoft or authorized security advisories. The vendor’s recommended patches or configuration changes are essential to mitigate this vulnerability. Until proper updates are applied, organizations should restrict access to SharePoint services, disable vulnerable features if possible, and monitor for unusual activities indicative of exploitation attempts.
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