CVE-2026-26118: Azure MCP Server SSRF Vulnerability

CVE-2026-26118 Overview

CVE-2026-26118 is a Server-Side Request Forgery (SSRF) vulnerability in Microsoft Azure MCP Server. The flaw allows an authorized attacker to elevate privileges over a network by coercing the server into issuing crafted requests to unintended internal endpoints. Microsoft assigned the issue to [CWE-918] and rated it High severity. The vulnerability affects multiple beta releases of Azure MCP Server 2.0.0 and earlier branches of the product line.

Critical Impact

An authenticated attacker can abuse the Azure MCP Server to reach internal resources and escalate privileges, with high impact on confidentiality, integrity, and availability.

Affected Products

• Microsoft Azure MCP Server (all versions prior to the fixed release)
• Microsoft Azure MCP Server 2.0.0 beta1 through beta16
• Deployments exposing the Azure MCP Server endpoint to authenticated network clients

Discovery Timeline

• 2026-03-10 - CVE-2026-26118 published to the National Vulnerability Database
• 2026-03-13 - Last updated in NVD database

Technical Details for CVE-2026-26118

Vulnerability Analysis

The Azure Model Context Protocol (MCP) Server brokers tool and resource calls between AI clients and Azure services. CVE-2026-26118 stems from insufficient validation of URLs or resource identifiers processed by the server. An authenticated attacker submits a request that causes the server to fetch attacker-controlled targets, including internal Azure metadata endpoints or services not exposed externally.

Because the MCP Server typically runs with elevated identity and network reachability, the forged request inherits that trust. This converts a low-privileged user session into a vector for accessing privileged endpoints. Microsoft classifies the outcome as privilege elevation over a network with high impact across confidentiality, integrity, and availability.

Root Cause

The root cause is improper validation of server-side outbound request destinations, consistent with [CWE-918]. The server accepts a user-supplied URL or identifier and dispatches a backend request without enforcing an allowlist or blocking internal network ranges. Attackers can target loopback addresses, link-local metadata services, and other endpoints reachable only from the server host.

Attack Vector

Exploitation requires network access and a low-privileged authenticated session. The attacker sends a crafted MCP request that instructs the server to retrieve or interact with an arbitrary URL. The server then proxies the request, returning content or triggering actions on internal services. No user interaction is required.

No verified public proof-of-concept code is available. Refer to the Microsoft CVE-2026-26118 Advisory for vendor technical details.

Detection Methods for CVE-2026-26118

Indicators of Compromise

• Outbound HTTP requests from the Azure MCP Server process to internal IP ranges such as 169.254.169.254, 127.0.0.1, or RFC1918 addresses not part of normal operation
• MCP Server log entries showing requests with user-supplied URL parameters resolving to metadata or management endpoints
• Anomalous spikes in authenticated MCP tool invocations from a single principal

Detection Strategies

• Inspect MCP Server access logs for request parameters containing URLs, hostnames, or schemes that target internal or cloud metadata services
• Correlate authenticated session identity with outbound network destinations and flag deviations from baseline behavior
• Enable Azure activity logging and review for token or credential retrieval calls originating from the MCP Server identity

Monitoring Recommendations

• Forward MCP Server logs, host network telemetry, and Azure control-plane events to a centralized analytics platform for correlation
• Alert on any request from the MCP Server host to the Instance Metadata Service (IMDS) endpoint
• Track privilege changes and role assignments tied to identities used by the MCP Server

How to Mitigate CVE-2026-26118

Immediate Actions Required

• Apply the security update referenced in the Microsoft CVE-2026-26118 Advisory as soon as available
• Restrict network egress from Azure MCP Server hosts using firewall rules or Network Security Groups
• Rotate credentials and tokens accessible to the MCP Server identity if compromise is suspected
• Limit MCP Server authentication to trusted principals and enforce least privilege on its managed identity

Patch Information

Microsoft has published guidance and update information through the Microsoft Security Response Center. Administrators should consult the Microsoft CVE-2026-26118 Advisory for fixed version numbers and deployment instructions. Update Azure MCP Server installations beyond the affected 2.0.0 beta range to the remediated build.

Workarounds

• Block outbound access from the MCP Server host to the Azure Instance Metadata Service endpoint 169.254.169.254 where the workload does not require it
• Constrain outbound traffic to an allowlist of required Azure service endpoints
• Disable or gate MCP Server features that accept user-supplied URLs until the patch is applied
• Require strong authentication and conditional access policies for clients invoking the MCP Server

# Example: restrict egress to IMDS using iptables on a Linux MCP Server host
iptables -A OUTPUT -d 169.254.169.254 -j DROP
iptables -A OUTPUT -d 127.0.0.0/8 ! -o lo -j DROP