CVE-2026-5607: mcp-browser-agent SSRF Vulnerability

CVE-2026-5607 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in imprvhub mcp-browser-agent versions up to 0.8.0. This security flaw impacts the function CallToolRequestSchema within the file src/handlers.ts of the URL Parameter Handler component. The vulnerability allows attackers to manipulate the request.params.name and request.params.arguments parameters to forge server-side requests, potentially enabling access to internal resources or services that should not be publicly accessible.

Critical Impact

Attackers can exploit this SSRF vulnerability remotely to make the server perform unintended requests to internal or external systems, potentially bypassing security controls and accessing sensitive internal resources.

Affected Products

• imprvhub mcp-browser-agent versions up to 0.8.0
• Applications utilizing the vulnerable CallToolRequestSchema function in src/handlers.ts
• Systems exposing the URL Parameter Handler component to untrusted input

Discovery Timeline

• April 6, 2026 - CVE-2026-5607 published to NVD
• April 7, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5607

Vulnerability Analysis

This vulnerability is classified as CWE-918 (Server-Side Request Forgery). The flaw exists in the URL Parameter Handler component of mcp-browser-agent, specifically within the CallToolRequestSchema function located in src/handlers.ts. The application fails to properly validate or sanitize user-controlled input passed through the request.params.name and request.params.arguments parameters before using them to construct server-side requests.

SSRF vulnerabilities of this nature allow attackers to abuse the server's functionality to access internal services, scan internal networks, or interact with cloud metadata services. The exploit has been publicly disclosed, and the vendor was contacted about this issue but did not respond.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the URL Parameter Handler component. The CallToolRequestSchema function in src/handlers.ts accepts user-supplied values for request.params.name and request.params.arguments without adequate sanitization or validation. This allows attackers to inject malicious URLs or parameters that cause the server to make unintended requests to arbitrary destinations, including internal network resources.

Attack Vector

The attack can be carried out remotely over the network. An authenticated attacker with low privileges can manipulate the vulnerable parameters to craft malicious requests. The exploitation flow involves:

1. An attacker identifies the vulnerable endpoint that processes URL parameters
2. The attacker crafts a malicious request containing a forged URL or internal resource reference in the request.params.name or request.params.arguments fields
3. The server processes this request without proper validation and executes the forged request
4. The attacker receives the response from the internal resource or observes the effects of the forged request

Technical details and proof-of-concept information can be found in the GitHub Issue Report and the VulDB Vulnerability Entry.

Detection Methods for CVE-2026-5607

Indicators of Compromise

• Unexpected outbound requests from the mcp-browser-agent server to internal IP addresses or localhost
• Requests to cloud metadata endpoints (e.g., 169.254.169.254) originating from the application server
• Unusual traffic patterns in the CallToolRequestSchema handler logs indicating attempts to access internal resources
• Error logs showing failed connections to internal services that should not be accessed by the application

Detection Strategies

• Implement network monitoring to detect outbound connections from the mcp-browser-agent server to internal network ranges (10.x.x.x, 172.16.x.x, 192.168.x.x)
• Configure application-level logging for the URL Parameter Handler to capture all incoming request parameters
• Deploy web application firewall (WAF) rules to detect SSRF patterns in request parameters
• Monitor for requests containing internal IP addresses, localhost references, or cloud metadata URLs in the request.params fields

Monitoring Recommendations

• Enable detailed access logging for the mcp-browser-agent application
• Set up alerts for any requests targeting internal network ranges or cloud metadata services
• Implement egress filtering and monitor for violations
• Review application logs regularly for suspicious URL patterns in the handler parameters

How to Mitigate CVE-2026-5607

Immediate Actions Required

• Upgrade mcp-browser-agent to a version newer than 0.8.0 when a patch becomes available
• Implement strict input validation for all URL parameters processed by the CallToolRequestSchema function
• Deploy network-level controls to restrict the server's ability to make requests to internal resources
• Consider implementing an allowlist of permitted destination URLs for server-side requests

Patch Information

At the time of publication, the vendor (imprvhub) has not responded to disclosure attempts, and no official patch information is available. Organizations should monitor the VulDB Vulnerability Entry and the project's GitHub repository for patch updates. Additional technical details can be found in the VulDB Submission.

Workarounds

• Implement URL validation that blocks requests to private IP ranges, localhost, and cloud metadata endpoints
• Deploy a web application firewall with SSRF-specific rules to filter malicious requests
• Restrict network egress from the application server to only necessary external destinations
• Apply the principle of least privilege to limit what internal resources the application can access
• Consider disabling or restricting access to the vulnerable URL Parameter Handler component until a patch is available

# Network-level mitigation: Block outbound access to internal ranges from the application server
# Example iptables rules (adjust for your environment)
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
iptables -A OUTPUT -d 127.0.0.0/8 -j DROP
iptables -A OUTPUT -d 169.254.169.254 -j DROP