Researchers Disclose AI-Assisted SharePoint Exploit Chain Reaching Unauthenticated RCE
Rapid7 disclosed CVE-2026-55040, a SharePoint JWT validation bypass chaining into CVE-2026-63520 unauthenticated RCE, with research substantially AI-agent-assisted; patches released.
Rapid7 disclosed CVE-2026-55040 (CVSS 9.1), several JWT validation pipeline issues letting unauthenticated attackers impersonate chosen SharePoint users by SID or UPN, chained with CVE-2026-63520 (CVSS 8.1), an unsafe .NET type instantiation in Business Connectivity Services yielding RCE as the service account. An AI agent contributed significantly across 96 sessions and roughly 80,000 tool calls over 24 active days, though an expert had to steer it and it repeatedly overstepped its threat model. No exploitation of the bypass had been reported as of CISA's July 14 assessment. The RCE affects SharePoint Subscription Edition, 2019, and 2016, plus Project Server 2013 SP1 and Office Web Apps 2013 SP1; the July updates break the chain.
- CVE-2026-55040: JWT validation flaws let an unauthenticated attacker act as any user identified by SID or UPN
- CVE-2026-63520: unsafe .NET type instantiation in Business Connectivity Services runs code as the service account
- July updates KB5002882/KB5002883/KB5002891 break the chain; install and hunt for IIS machine key theft
- SharePoint 2016 and 2019 passed end of support on July 14; future fixes for them are unresolved
- Agent sessions included 256 prompts and ~80,000 tool calls; researcher steering was required
Vulnerabilities mentioned
All| CVE | Vulnerability | CVSS | EPSS | Signals | Published |
|---|---|---|---|---|---|
| CVE-2026-55040 | Authentication Bypass in Microsoft SharePoint Server | 9.1 | 70% | KEVPoC ×2 | KEV |
| CVE-2026-63520 | Unauthenticated RCE in Microsoft SharePoint Server | 8.1 | 3% |
From the original article
3 min read at thehackernews.com
Swati Khandelwal Aug 11, 2026 Vulnerability / Enterprise Security Security researchers found a way to enter Microsoft SharePoint servers as any user, including an administrator, with no valid account. A significant part of the work that found it was done through an AI agent. The flaw, tracked as CVE-2026-55040 (CVSS 9.
By @TheHackersNews · thehackernews.com
A short excerpt; the article and its images belong to the publisher. Summary, key facts and assessment above are AI-written from the article and can be wrong.