CVE-2026-6599: Langflow-AI Langflow SSRF Vulnerability

CVE-2026-6599 Overview

A header injection vulnerability has been identified in langflow-ai Langflow versions up to 1.8.3. The vulnerability exists in the get_client_ip and install_mcp_config functions within the Model Context Protocol (MCP) Configuration API component. An attacker can exploit this flaw by manipulating the X-Forwarded-For HTTP header to inject malicious content, potentially leading to security bypasses or unauthorized access.

Critical Impact

Remote attackers can exploit this injection vulnerability via crafted HTTP headers to potentially bypass IP-based access controls or inject malicious data through the MCP Configuration API.

Affected Products

• langflow-ai Langflow up to version 1.8.3
• Model Context Protocol Configuration API component
• File: src/backend/base/langflow/api/v1/mcp_projects.py

Discovery Timeline

• 2026-04-20 - CVE-2026-6599 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6599

Vulnerability Analysis

This vulnerability is classified as CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), commonly known as injection. The affected functions get_client_ip and install_mcp_config in the MCP Configuration API fail to properly sanitize the X-Forwarded-For header before processing it.

The X-Forwarded-For header is commonly used in web applications behind load balancers or reverse proxies to identify the originating IP address of a client. When applications trust this header without proper validation, attackers can inject arbitrary values that may be processed downstream, leading to security control bypasses or data injection.

The vulnerability affects the network-accessible API endpoint, requiring only low-level authentication to exploit. While the immediate impact on confidentiality, integrity, and availability is considered limited, the injection nature of this vulnerability opens the door for various attack scenarios depending on how the injected data is processed by downstream components.

Root Cause

The root cause lies in insufficient input validation and sanitization of the X-Forwarded-For HTTP header in the get_client_ip and install_mcp_config functions. The application directly processes header values without neutralizing special elements that could be interpreted as control characters or commands by downstream systems.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An authenticated attacker with low privileges can send crafted HTTP requests to the MCP Configuration API endpoint with a malicious X-Forwarded-For header value. The vulnerability requires no user interaction and can be exploited with low attack complexity.

The exploitation involves crafting HTTP requests with specially formed header values that, when processed by the vulnerable functions, result in injection of unintended data or commands. The exploit has been publicly disclosed, increasing the risk of active exploitation.

For technical details regarding the exploit mechanism, see the GitHub Gist Exploit Code and the VulDB vulnerability entry.

Detection Methods for CVE-2026-6599

Indicators of Compromise

• Unusual or malformed X-Forwarded-For header values in HTTP request logs
• Multiple requests to /api/v1/mcp_projects endpoints with varying header content
• Unexpected IP address patterns or injection strings in application logs
• Signs of IP spoofing or access control bypass attempts

Detection Strategies

• Implement web application firewall (WAF) rules to detect malformed or suspicious X-Forwarded-For header values
• Monitor API access logs for unusual patterns targeting the MCP Configuration API endpoints
• Deploy intrusion detection signatures that identify header injection attempts
• Review authentication logs for access anomalies that may indicate IP-based control bypasses

Monitoring Recommendations

• Enable verbose logging on the Langflow application to capture all incoming HTTP headers
• Set up alerts for requests containing special characters or injection patterns in header fields
• Monitor for unauthorized configuration changes in the MCP projects module
• Implement rate limiting on the affected API endpoints to slow potential exploitation attempts

How to Mitigate CVE-2026-6599

Immediate Actions Required

• Update langflow-ai Langflow to a patched version when available from the vendor
• Implement strict input validation for the X-Forwarded-For header at the web server or proxy level
• Restrict access to the MCP Configuration API endpoints to trusted networks or IP addresses
• Deploy WAF rules to filter malicious header values before they reach the application

Patch Information

At the time of publication, the vendor has not responded to disclosure attempts and no official patch has been released. Organizations should monitor the langflow-ai project for security updates and apply patches as soon as they become available. Additional vulnerability details can be found in the VulDB submission.

Workarounds

• Configure reverse proxy or load balancer to sanitize and validate X-Forwarded-For headers before forwarding to the application
• Implement network-level access controls to limit exposure of the MCP Configuration API
• Use allowlist-based IP validation at the proxy layer rather than relying on application-level header parsing
• Consider disabling the affected MCP Configuration API functionality if not required for operations

# Example: Nginx configuration to sanitize X-Forwarded-For header
# Add to nginx.conf or site configuration

# Clear any client-supplied X-Forwarded-For and set it to the real client IP
proxy_set_header X-Forwarded-For $remote_addr;

# Alternatively, validate the header format using a map
map $http_x_forwarded_for $validated_xff {
    default "";
    "~^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$" $http_x_forwarded_for;
}
proxy_set_header X-Forwarded-For $validated_xff;