Rapid7 Labs and Microsoft have disclosed CVE-2026-63520, a Remote Code Execution vulnerability in Microsoft SharePoint caused by an unsafe .NET type instantiation in Business Connectivity Services. With a CVSSv3.1 score of 8.1 (High), it affects all supported SharePoint versions, Project Server, and Office Web Apps Server. When chained with the previously disclosed authentication bypass CVE-2026-55040, it enables unauthenticated RCE against vulnerable SharePoint servers. The exploit chain was developed using an AI-assisted agentic workflow guided by subject matter experts, accumulating 120 hours of agent runtime, 96 sessions, ~80,000 tool calls, and 256 prompts over 24 days. The research was originally entered into Pwn2Own Berlin. Patches are available; customers should apply the latest SharePoint updates immediately. Full technical details for the RCE will be published within 30 days of disclosure.
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OverviewWorkflowProduct descriptionsImpactCreditVendor statementTechnical analysisRemediationRapid7 customersDisclosure timelineQuestions this post answers
What is CVE-2026-63520 and how severe is it?
CVE-2026-63520 is a Remote Code Execution vulnerability in Microsoft SharePoint caused by an unsafe .NET type instantiation in Business Connectivity Services. It carries a CVSSv3.1 score of 8.1 (High) and allows arbitrary code execution with the privileges of the SharePoint Site's service account. When chained with the authentication bypass CVE-2026-55040, it enables unauthenticated RCE against vulnerable SharePoint servers. Teams managing SharePoint deployments track exploit chains like this on daily.dev before patches reach their environments.
Which Microsoft products are affected by CVE-2026-63520?
CVE-2026-63520 affects Microsoft SharePoint Server Subscription Edition, SharePoint Server 2019, SharePoint Enterprise Server 2016, Microsoft Project Server 2013 SP1 (64-bit), and Microsoft Office Web Apps 2013 SP1. The companion authentication bypass CVE-2026-55040 affects SharePoint only. Microsoft has released patches; applying the latest available updates for each impacted product is the recommended remediation. Security engineers patching enterprise Microsoft stacks find coordinated disclosures like this faster on daily.dev.
How did Rapid7 use AI to discover the SharePoint RCE exploit chain?
Rapid7 used an agentic LLM workflow guided by subject matter experts, running from January through March. The agent accumulated 120 hours of runtime over 24 days, leveraged 96 sessions, generated approximately 80,000 tool calls, and required 256 human-issued prompts. A fully automated approach proved insufficient — the agent frequently produced inaccurate findings or overstepped its scope, making expert steering essential to reach a working unauthenticated RCE chain. Researchers exploring AI-assisted vulnerability discovery follow methodology developments like this on daily.dev.