CVE-2026-3683: Bufanyun HotGo SSRF Vulnerability

CVE-2026-3683 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in bufanyun HotGo versions up to 2.0. This vulnerability affects the ImageTransferStorage function within the file /server/internal/logic/common/upload.go of the Endpoint component. An attacker can exploit this flaw remotely to manipulate server-side requests, potentially accessing internal resources or pivoting to attack other systems within the network.

Critical Impact

Remote attackers with low privileges can exploit this SSRF vulnerability to force the server to make requests to arbitrary internal or external destinations, potentially leading to internal network reconnaissance, data exfiltration, or access to cloud metadata services.

Affected Products

• bufanyun HotGo up to version 2.0
• Systems running the vulnerable ImageTransferStorage endpoint
• Deployments exposing the /server/internal/logic/common/upload.go functionality

Discovery Timeline

• 2026-03-08 - CVE-2026-3683 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3683

Vulnerability Analysis

The vulnerability resides in the ImageTransferStorage function within HotGo's upload handling logic. This function processes user-supplied URLs for image transfer operations without properly validating the destination. The lack of input validation allows attackers to specify arbitrary URLs, causing the server to initiate requests to attacker-controlled or internal network destinations. This is classified as CWE-918 (Server-Side Request Forgery).

The network-accessible attack vector allows remote exploitation with low privileges required. The vulnerability can result in limited impact to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of this vulnerability is insufficient validation of user-supplied URL parameters in the ImageTransferStorage function. The application accepts external URLs for image transfer operations but fails to implement proper allowlist validation, URL scheme restrictions, or destination filtering. This allows attackers to supply malicious URLs that cause the server to make unintended requests.

Attack Vector

The vulnerability can be exploited remotely over the network. An authenticated attacker with low privileges can submit crafted requests to the vulnerable endpoint, specifying internal network addresses or cloud metadata endpoints (such as http://169.254.169.254/) as the target URL. The server processes these requests and returns the response data to the attacker, enabling internal network scanning, access to sensitive metadata, or interaction with internal services that should not be externally accessible.

The exploitation mechanism involves manipulating the image URL parameter in requests to the ImageTransferStorage function. When the server fetches the specified URL to transfer an image, it does so using its own network context, bypassing firewall restrictions that would normally prevent external access to internal resources.

Detection Methods for CVE-2026-3683

Indicators of Compromise

• Unusual outbound requests from the HotGo server to internal IP ranges (10.x.x.x, 172.16.x.x-172.31.x.x, 192.168.x.x)
• Requests to cloud metadata endpoints (169.254.169.254) originating from the application server
• Unexpected DNS lookups or HTTP requests to localhost or loopback addresses from the upload endpoint
• Access logs showing repeated requests to the ImageTransferStorage endpoint with external or suspicious URLs

Detection Strategies

• Monitor server-side outbound connections for requests to internal network ranges or known metadata endpoints
• Implement web application firewall (WAF) rules to detect SSRF attack patterns in URL parameters
• Review application logs for the upload endpoint showing unusual URL patterns or high request volumes
• Deploy network segmentation monitoring to detect lateral movement attempts from the application server

Monitoring Recommendations

• Enable verbose logging for the ImageTransferStorage function to capture all URL parameters
• Configure alerting for outbound connections from the HotGo application server to internal network segments
• Monitor for responses containing cloud provider metadata or internal service information
• Implement anomaly detection for unusual URL schemes (file://, gopher://, dict://) in upload requests

How to Mitigate CVE-2026-3683

Immediate Actions Required

• Restrict network access to the HotGo server's outbound connections using firewall rules
• Implement URL allowlisting for the ImageTransferStorage function to only permit trusted domains
• Disable or restrict access to the vulnerable endpoint if not required for business operations
• Monitor for exploitation attempts using the detection strategies outlined above

Patch Information

The vendor (bufanyun) was contacted early about this disclosure but did not respond. As of the last update, no official patch is available. Organizations should implement workarounds and monitor for vendor updates through the GitHub vulnerability repository and VulDB entry for any forthcoming patches or additional technical guidance.

Workarounds

• Implement a reverse proxy with URL validation to filter requests before they reach the ImageTransferStorage endpoint
• Configure network-level egress filtering to block the server from initiating connections to internal IP ranges and cloud metadata services
• Add application-level URL validation to enforce allowlisted domains for image transfer operations
• Consider disabling the image transfer functionality entirely until a patch is available if not business-critical

# Example iptables rules to restrict outbound SSRF attempts
# Block outbound connections to common internal ranges from the application server
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 169.254.169.254 -j DROP
iptables -A OUTPUT -d 127.0.0.0/8 -j DROP