CVE-2026-7221: TencentCloudBase CloudBase-MCP SSRF Flaw

CVE-2026-7221 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in TencentCloudBase CloudBase-MCP versions up to 2.17.0. The vulnerability exists in the openUrl function within the mcp/src/interactive-server.ts file, specifically in the open-url API Endpoint. By manipulating the req.body.url parameter, an attacker can force the server to make requests to arbitrary internal or external resources, potentially accessing sensitive internal services, cloud metadata endpoints, or other protected network resources.

Critical Impact

Remote attackers can exploit this SSRF vulnerability to bypass network security controls, access internal services, retrieve cloud instance metadata, and potentially pivot to other systems within the network infrastructure.

Affected Products

• TencentCloudBase CloudBase-MCP versions up to 2.17.0
• Applications using the open-url API Endpoint in CloudBase-MCP
• Deployments exposing the interactive-server.ts component to untrusted input

Discovery Timeline

• 2026-04-28 - CVE CVE-2026-7221 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-7221

Vulnerability Analysis

This vulnerability is classified as CWE-918 (Server-Side Request Forgery). The SSRF flaw occurs when the openUrl function in the interactive server accepts user-controlled URL input without proper validation. The application fails to sanitize or restrict the URLs that can be requested, allowing attackers to manipulate the server into making requests to unintended destinations.

SSRF vulnerabilities are particularly dangerous in cloud environments where they can be leveraged to access cloud provider metadata services (e.g., metadata.google.internal, AWS metadata at 169.254.169.254), potentially exposing sensitive credentials, API keys, and infrastructure configuration details.

Root Cause

The root cause of this vulnerability lies in insufficient input validation of the req.body.url parameter in the openUrl function. Prior to version 2.17.1, the application did not implement proper URL scheme restrictions or hostname validation, allowing attackers to specify arbitrary URLs including those targeting internal network resources, localhost services, and cloud metadata endpoints.

Attack Vector

The attack can be launched remotely over the network without requiring authentication. An attacker sends a crafted request to the open-url API endpoint with a malicious URL in the request body. The server then processes this URL and makes an outbound request on behalf of the attacker, effectively bypassing firewall rules and network segmentation that would normally prevent direct access to internal resources.

Common exploitation targets include:

• Cloud provider metadata services for credential theft
• Internal APIs and microservices not exposed to the internet
• Administrative interfaces on localhost
• Internal network scanning and enumeration

// Security patch implementing URL validation (from actual fix)
/**
 * Validates that a URL is safe to open, blocking SSRF targets.
 * Only allows http/https schemes and rejects private/reserved IP ranges
 * and sensitive hostnames.
 */
function isUrlSafeToOpen(url: string): { safe: boolean; reason?: string } {
  let parsed: URL;
  try {
    parsed = new URL(url);
  } catch {
    return { safe: false, reason: "Invalid URL format" };
  }

  // Only allow http and https schemes
  if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
    return { safe: false, reason: `Unsupported scheme: ${parsed.protocol}` };
  }

  const hostname = parsed.hostname.toLowerCase();

  // Block common sensitive / internal hostnames
  const blockedHostnames = [
    "localhost",
    "localhost.localdomain",
    "ip6-localhost",
    "ip6-loopback",
    "metadata.google.internal",
    // ... additional blocked hostnames
  ];
  // ... validation continues
}

Source: GitHub Commit Changes

Detection Methods for CVE-2026-7221

Indicators of Compromise

• Unusual outbound requests from the CloudBase-MCP server to internal IP ranges (10.x.x.x, 172.16.x.x, 192.168.x.x)
• Requests to cloud metadata endpoints such as 169.254.169.254 or metadata.google.internal
• Unexpected traffic to localhost (127.0.0.1) or IPv6 loopback addresses from the application server
• API requests containing URLs with non-standard schemes (file://, gopher://, dict://)

Detection Strategies

• Monitor network traffic from CloudBase-MCP servers for connections to internal network ranges that shouldn't be accessed
• Implement web application firewall (WAF) rules to detect and block SSRF payloads in the url parameter
• Review application logs for suspicious URL patterns in requests to the open-url endpoint
• Deploy network segmentation monitoring to detect lateral movement attempts originating from the application tier

Monitoring Recommendations

• Enable verbose logging for all requests to the open-url API endpoint
• Configure alerts for outbound connections from the application server to sensitive internal services
• Monitor for failed connection attempts to internal IP addresses that may indicate reconnaissance activity
• Implement anomaly detection for unusual URL patterns or high volumes of requests to the vulnerable endpoint

How to Mitigate CVE-2026-7221

Immediate Actions Required

• Upgrade TencentCloudBase CloudBase-MCP to version 2.17.1 or later immediately
• If immediate upgrade is not possible, disable or restrict access to the open-url API endpoint
• Implement network-level controls to prevent the application server from accessing internal services and cloud metadata endpoints
• Review logs for any evidence of exploitation prior to patching

Patch Information

The vulnerability has been addressed in CloudBase-MCP version 2.17.1. The fix, identified by commit hash 3f678a1e7bd400cd76469d61024097d4920dc6b5, implements proper URL validation through the isUrlSafeToOpen function. This function restricts URL schemes to http/https only and blocks requests to localhost, loopback addresses, private IP ranges, and sensitive cloud metadata hostnames.

For detailed patch information, see:

• GitHub Release Notes for v2.17.1
• GitHub Pull Request #510
• GitHub Issue Discussion #509

Workarounds

• Implement a reverse proxy or WAF in front of the application to filter and validate URLs before they reach the vulnerable endpoint
• Configure network-level firewall rules to block outbound connections from the application server to internal networks and cloud metadata services
• Disable the open-url API endpoint entirely if it is not required for application functionality
• Deploy network segmentation to isolate the CloudBase-MCP application from sensitive internal resources

# Example: Block metadata service access using iptables
# Run on the CloudBase-MCP application server
iptables -A OUTPUT -d 169.254.169.254 -j DROP
iptables -A OUTPUT -d 169.254.0.0/16 -j DROP

# Block access to common internal networks from the application
iptables -A OUTPUT -d 10.0.0.0/8 -p tcp --dport 80 -j DROP
iptables -A OUTPUT -d 172.16.0.0/12 -p tcp --dport 80 -j DROP
iptables -A OUTPUT -d 192.168.0.0/16 -p tcp --dport 80 -j DROP