CVE-2026-47645: Microsoft 365 Copilot Business Chat Open Redirect Privilege Escalation

Technical summary

The vulnerability exists as an unvalidated URL redirection flaw (CWE-601) in Microsoft 365 Copilot's Business Chat component. An attacker can inject a crafted URL that appears legitimate within the chat interface but redirects users to an untrusted external site. The flaw allows privilege escalation over the network without requiring prior authentication. The CVSS 3.1 score of 8.8 (HIGH) reflects network-based exploitation, low complexity, no privilege requirements, and potential for complete compromise of confidentiality, integrity, and availability. The attack vector requires user interaction but is otherwise unrestricted in scope.

Business impact

This vulnerability threatens organizations' ability to securely use Microsoft 365 Copilot for internal collaboration and decision-making. Employees deceived into following malicious links could expose sensitive corporate data, enable credential theft, or provide attackers a foothold for lateral movement within the organization. For enterprises managing sensitive communications through Copilot—particularly in finance, legal, or strategic planning—unauthorized privilege escalation poses a material risk to governance and data integrity. The requirement for user interaction may reduce mass-exploitation risk but does not eliminate the threat posed by targeted social engineering campaigns.

Affected systems

Microsoft 365 Copilot, specifically the Business Chat feature, is affected. Organizations operating this service should assume all instances are vulnerable until patched. Confirm your deployment scope by reviewing Copilot enablement settings within your Microsoft 365 tenant and identifying which users have Business Chat access.

Exploitability

Exploitation is practical and requires moderate attacker sophistication. The attacker must craft a malicious link and deliver it to a target—either directly through chat, email, or social engineering. No zero-click behavior is present; victims must consciously click the link. However, because Business Chat operates within a trusted corporate environment where users may lower their guard, social engineering success rates could be elevated. The attack does not require authentication or special configuration, making it broadly applicable once a victim is identified.

Remediation

Apply the security update from Microsoft as soon as it becomes available. Until patching is complete, organizations should consider disabling Business Chat or restricting its availability to lower-risk user populations. Implement complementary controls: educate users on open redirect risks, enforce email link warnings and URL scanning, monitor for suspicious redirect patterns in logs, and enforce multi-factor authentication to reduce the impact of compromised credentials resulting from credential-harvesting redirects.

Patch guidance

Monitor the Microsoft Security Update Guide and your Microsoft 365 admin center for official patches to Copilot. Verify patches through the vendor advisory before deployment. Test patches in a non-production environment first, as Copilot updates can affect user workflows. Coordinate with stakeholders who depend on Business Chat to plan maintenance windows. Once patches are available, prioritize rapid deployment due to the HIGH severity rating and the ease of social engineering in a business context.

Detection guidance

Monitor network logs for unexpected outbound redirects or URL rewrites originating from Copilot infrastructure. Capture HTTP referrer logs from Business Chat interactions and flag any redirects to external, non-corporate domains. Implement Conditional Access policies to flag Business Chat sessions that redirect to untrusted URLs. Review user feedback and phishing reports for mentions of suspicious Copilot links. Consider UEBA (User and Entity Behavior Analytics) to detect unusual post-redirect activity patterns, such as rapid credential usage or privilege escalation attempts following a redirect event.

Why prioritize this

This vulnerability merits immediate attention due to its HIGH CVSS score, lack of complex exploitation barriers, and the privileged trust users place in internal collaboration tools. While not yet in the CISA KEV catalog, the combination of network exploitability, high impact, and social engineering potential makes it a prime target for adversaries seeking to compromise organizations at scale. Prioritization should reflect both the technical severity and the organizational dependence on Copilot for business-critical communications.

Risk score, explained

The CVSS 3.1 score of 8.8 reflects a network-accessible vulnerability with low attack complexity, no authentication requirement, and high impact across confidentiality, integrity, and availability. The requirement for user interaction (UI:R) prevents a perfect 9.8 score but does not significantly reduce risk in a social engineering context. The 'unchanged scope' (S:U) indicates the vulnerability is confined to the Copilot component itself, though privilege escalation outcomes can extend impact beyond that boundary.

Frequently asked questions