CVE-2026-32110: SiYuan SSRF Vulnerability

CVE-2026-32110 Overview

CVE-2026-32110 is a Server-Side Request Forgery (SSRF) vulnerability in SiYuan, a personal knowledge management system. Prior to version 3.6.0, the /api/network/forwardProxy endpoint allows authenticated users to make arbitrary HTTP requests from the server. The endpoint accepts a user-controlled URL and makes HTTP requests to it, returning the full response body and headers. There is no URL validation to prevent requests to internal networks, localhost, or cloud metadata services.

Critical Impact

Authenticated attackers can leverage this SSRF vulnerability to access internal services, cloud metadata endpoints, and sensitive resources that should not be accessible from external networks, potentially leading to credential theft and further system compromise.

Affected Products

• SiYuan versions prior to 3.6.0

Discovery Timeline

• 2026-03-11 - CVE CVE-2026-32110 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-32110

Vulnerability Analysis

This vulnerability is classified as CWE-918 (Server-Side Request Forgery). The /api/network/forwardProxy endpoint in SiYuan functions as an open proxy, accepting user-controlled URLs and forwarding HTTP requests on behalf of the server. When exploited, the server acts as a proxy to internal resources, bypassing network segmentation and firewall protections.

The vulnerability is particularly dangerous because the endpoint returns both the full response body and headers from the target URL. This allows attackers to extract sensitive information from internal services, including cloud instance metadata services (such as AWS IMDSv1 at http://169.254.169.254/), internal APIs, and services running on localhost.

Root Cause

The root cause of this vulnerability is insufficient input validation on the URL parameter passed to the /api/network/forwardProxy endpoint. The application fails to implement URL allowlisting or denylisting to restrict requests to approved external domains. Without proper validation, the server will fetch any URL provided by an authenticated user, including internal network addresses, localhost services, and cloud provider metadata endpoints.

Attack Vector

The attack requires network access and low-level authentication (any authenticated user). An attacker can exploit this vulnerability by sending crafted requests to the /api/network/forwardProxy endpoint with malicious URLs targeting internal resources. The attack does not require user interaction and can be automated.

Potential attack scenarios include:

• Accessing cloud instance metadata to steal IAM credentials
• Scanning internal networks to discover services
• Accessing internal APIs and administrative interfaces
• Retrieving sensitive configuration files from internal services
• Bypassing IP-based access controls on internal resources

The vulnerability mechanism involves the forwardProxy endpoint accepting a URL parameter and making an HTTP request to that URL from the server's network context. Since no validation is performed, attackers can specify internal IP addresses, localhost, or cloud metadata service URLs. For technical details, see the GitHub Security Advisory.

Detection Methods for CVE-2026-32110

Indicators of Compromise

• HTTP requests to the /api/network/forwardProxy endpoint containing internal IP addresses (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
• Requests targeting cloud metadata services (e.g., 169.254.169.254, metadata.google.internal)
• Unusual outbound connections from the SiYuan server to internal services
• Authentication logs showing users making repeated proxy requests to different internal addresses

Detection Strategies

• Monitor web application logs for requests to /api/network/forwardProxy with suspicious URL parameters
• Implement network monitoring to detect connections from the SiYuan server to internal services or metadata endpoints
• Deploy web application firewall (WAF) rules to block SSRF patterns in request parameters
• Use SentinelOne Singularity XDR to correlate network behavior anomalies with application-layer events

Monitoring Recommendations

• Enable detailed logging for all requests to the /api/network/forwardProxy endpoint
• Configure alerting for any requests containing private IP ranges or cloud metadata addresses
• Monitor for unusual data exfiltration patterns from the SiYuan server
• Implement DNS query logging to detect resolution of internal hostnames through the proxy

How to Mitigate CVE-2026-32110

Immediate Actions Required

• Upgrade SiYuan to version 3.6.0 or later immediately
• If upgrading is not immediately possible, restrict access to the /api/network/forwardProxy endpoint at the network or reverse proxy level
• Review access logs for signs of exploitation targeting internal resources
• Rotate any credentials that may have been accessible through internal services or cloud metadata

Patch Information

The vulnerability is fixed in SiYuan version 3.6.0. Users should upgrade to this version or later to remediate the vulnerability. For more information, see the GitHub Security Advisory.

Workarounds

• Block or restrict access to the /api/network/forwardProxy endpoint using a reverse proxy or WAF
• Implement network segmentation to limit the SiYuan server's ability to reach internal services
• If running in a cloud environment, enable IMDSv2 with hop limit of 1 to prevent metadata theft
• Apply IP allowlisting at the network level to restrict which users can access SiYuan

# Example nginx configuration to block the vulnerable endpoint
location /api/network/forwardProxy {
    deny all;
    return 403;
}