CVE-2026-26137: Microsoft 365 Copilot SSRF Vulnerability

CVE-2026-26137 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in Microsoft 365 Copilot's Business Chat feature. This vulnerability allows an authorized attacker to craft malicious requests that can be forwarded by the server to internal resources, potentially enabling privilege escalation over a network. The SSRF flaw can be exploited to access internal services, bypass security controls, and escalate privileges within the Microsoft 365 environment.

Critical Impact

An authenticated attacker can leverage this SSRF vulnerability to escalate privileges across the network, potentially accessing sensitive internal resources and compromising the confidentiality and integrity of enterprise data within Microsoft 365 Copilot environments.

Affected Products

• Microsoft 365 Copilot Business Chat

Discovery Timeline

• 2026-03-19 - CVE-2026-26137 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-26137

Vulnerability Analysis

This vulnerability is classified as CWE-918 (Server-Side Request Forgery), a weakness where an application can be tricked into making requests to unintended destinations. In the context of Microsoft 365 Copilot's Business Chat, the SSRF vulnerability allows an authenticated attacker to manipulate server-side requests, redirecting them to internal services or external malicious endpoints.

The attack requires network access and user interaction, with the potential to affect resources beyond the vulnerable component's security scope. The vulnerability can result in high impact to both confidentiality and integrity of the affected system, with a lower but still notable impact on availability.

Root Cause

The root cause of this vulnerability lies in insufficient validation and sanitization of user-controlled input that influences server-side HTTP requests within the Business Chat feature. When the application processes requests without properly validating the destination URL or restricting which internal resources can be accessed, it creates an SSRF condition. The lack of proper URL allowlisting or blocklisting mechanisms enables attackers to redirect requests to arbitrary destinations, including internal network services that should not be directly accessible.

Attack Vector

The attack vector for CVE-2026-26137 is network-based, requiring the attacker to have authorized access to Microsoft 365 Copilot. The attacker can craft specially formatted requests through the Business Chat interface that manipulate the server into making requests to internal resources or services. This can be leveraged to:

1. Access internal metadata services and cloud infrastructure endpoints
2. Probe internal network services and gather reconnaissance information
3. Bypass network security controls and firewalls
4. Escalate privileges by accessing internal APIs with elevated permissions
5. Potentially pivot to other internal systems within the organization's network

The vulnerability requires some user interaction, making it a two-stage attack where the attacker must first establish authorized access before exploiting the SSRF condition.

Detection Methods for CVE-2026-26137

Indicators of Compromise

• Unusual outbound requests from Microsoft 365 Copilot services to internal IP addresses or localhost endpoints
• Requests to cloud metadata endpoints (e.g., 169.254.169.254) originating from Business Chat components
• Anomalous network traffic patterns indicating internal service probing or reconnaissance activity

Detection Strategies

• Monitor Microsoft 365 audit logs for suspicious Business Chat activity, particularly requests with unusual URL patterns or internal IP references
• Implement network traffic analysis to detect server-side requests to non-standard destinations from Copilot services
• Deploy web application firewall (WAF) rules to identify and block SSRF patterns in request payloads

Monitoring Recommendations

• Enable enhanced logging for Microsoft 365 Copilot services and correlate with SIEM solutions
• Configure alerts for access attempts to internal infrastructure endpoints from cloud-hosted services
• Review Microsoft 365 Defender signals for indicators of SSRF exploitation attempts

How to Mitigate CVE-2026-26137

Immediate Actions Required

• Review and apply the latest security updates from Microsoft for Microsoft 365 Copilot
• Audit user access to Business Chat features and restrict to necessary personnel
• Implement additional network segmentation to limit the impact of potential SSRF exploitation
• Monitor for suspicious activity using the detection methods outlined above

Patch Information

Microsoft has released a security update addressing this vulnerability. Organizations should apply the patch immediately through their standard Microsoft 365 update channels. For detailed patch information and deployment guidance, refer to the Microsoft Security Update for CVE-2026-26137.

Workarounds

• Implement strict network segmentation to prevent compromised services from accessing sensitive internal resources
• Configure outbound request filtering at the network level to block requests to internal IP ranges from cloud services
• Consider temporarily restricting Business Chat functionality for high-risk users until the patch is applied

# Example: Network-level mitigation - Block internal IP access from cloud services
# Configure firewall rules to prevent SSRF exploitation
# Note: Adapt these rules to your specific network configuration

# Block access to internal metadata endpoints
iptables -A OUTPUT -d 169.254.169.254 -j DROP

# Block access to private IP ranges from cloud-connected services
iptables -A OUTPUT -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -d 192.168.0.0/16 -j DROP