CVE-2024-1021: Ruifang-tech Rebuild SSRF Vulnerability

CVE-2024-1021 Overview

A critical Server-Side Request Forgery (SSRF) vulnerability has been identified in Ruifang-tech Rebuild up to version 3.5.5. The vulnerability exists within the readRawText function of the HTTP Request Handler component, where improper validation of the url argument allows attackers to forge server-side requests. This flaw enables remote attackers to manipulate the application into making arbitrary HTTP requests to internal or external systems, potentially exposing sensitive data, bypassing access controls, or facilitating further attacks on internal infrastructure.

Critical Impact

This SSRF vulnerability allows unauthenticated remote attackers to forge arbitrary server-side requests, potentially accessing internal services, exfiltrating sensitive data, or pivoting to attack internal network resources. The exploit has been publicly disclosed, significantly increasing the risk of active exploitation.

Affected Products

• Ruifang-tech Rebuild versions up to and including 3.5.5
• Applications utilizing the vulnerable HTTP Request Handler component
• Systems with network access to the Rebuild application

Discovery Timeline

• 2024-01-29 - CVE-2024-1021 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-1021

Vulnerability Analysis

The vulnerability resides in the readRawText function within Rebuild's HTTP Request Handler component. This function is designed to fetch and process content from user-supplied URLs. However, the implementation fails to properly validate and sanitize the url parameter before initiating server-side HTTP requests.

Server-Side Request Forgery (SSRF) vulnerabilities of this nature are particularly dangerous because they allow attackers to abuse the trust relationships that exist between the vulnerable server and internal network resources. The application server effectively becomes a proxy for the attacker, capable of accessing resources that would otherwise be protected by network segmentation or firewall rules.

The vulnerability is classified under CWE-918 (Server-Side Request Forgery), which describes weaknesses where an attacker can influence the server to make requests to arbitrary domains, including internal infrastructure components such as metadata services, internal APIs, and other sensitive endpoints.

Root Cause

The root cause of this vulnerability is insufficient input validation and sanitization of the url parameter passed to the readRawText function. The HTTP Request Handler does not implement proper URL validation controls such as:

• Allowlisting of permitted domains or IP ranges
• Blocking of internal IP address ranges (127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
• Protocol restrictions to prevent exploitation via alternative schemes (file://, gopher://, dict://)
• DNS rebinding protections to prevent bypass of IP-based restrictions

Attack Vector

The attack can be launched remotely over the network without requiring any authentication or user interaction. An attacker can craft malicious HTTP requests containing specially designed URL payloads targeting the vulnerable readRawText function.

The vulnerability can be exploited to:

• Access internal services and APIs not exposed to the internet
• Query cloud metadata endpoints (e.g., AWS EC2 metadata at 169.254.169.254)
• Scan internal network ports and discover services
• Retrieve sensitive configuration files using file:// protocol
• Bypass firewall and network access controls

The attack involves sending a crafted HTTP request to the Rebuild application with a malicious url parameter pointing to internal resources. For example, an attacker might target internal metadata services, localhost services, or internal APIs. The server processes this request and returns the response content to the attacker, effectively leaking internal information. For detailed technical information, refer to the Yuque Security Document.

Detection Methods for CVE-2024-1021

Indicators of Compromise

• HTTP requests containing internal IP addresses or localhost references in URL parameters
• Requests to cloud metadata endpoints (169.254.169.254) originating from the Rebuild application
• Unusual outbound connections from the Rebuild server to internal network ranges
• Log entries showing access to the readRawText function with suspicious URL values

Detection Strategies

• Monitor application logs for requests to the HTTP Request Handler with URL parameters containing private IP ranges (10.x.x.x, 172.16-31.x.x, 192.168.x.x, 127.x.x.x)
• Implement network traffic analysis to detect unusual server-initiated connections to internal services
• Deploy web application firewall (WAF) rules to block SSRF payloads in request parameters
• Configure intrusion detection systems to alert on cloud metadata access patterns

Monitoring Recommendations

• Enable verbose logging for the HTTP Request Handler component to capture all URL parameters
• Set up real-time alerting for outbound connections from the Rebuild server to sensitive internal endpoints
• Monitor DNS queries from the application server for suspicious internal hostname lookups
• Review application access logs regularly for patterns indicative of SSRF exploitation attempts

How to Mitigate CVE-2024-1021

Immediate Actions Required

• Upgrade Ruifang-tech Rebuild to a version higher than 3.5.5 if a patched version is available
• Implement network-level controls to restrict outbound connections from the Rebuild application server
• Deploy a web application firewall (WAF) with SSRF protection rules
• Disable or restrict access to the vulnerable readRawText functionality if not required

Patch Information

Organizations should monitor the vendor's official channels for security patches addressing this vulnerability. Additional technical details can be found in the VulDB Entry #252290 and the VulDB CTI Indicator. As the exploit has been publicly disclosed, applying patches should be treated as a high priority.

Workarounds

• Implement strict URL allowlisting at the application or proxy level to only permit requests to known-safe domains
• Block outbound connections from the Rebuild server to internal IP ranges using firewall rules
• Configure the application server to use a forward proxy that enforces URL restrictions and blocks access to private IP ranges
• If feasible, disable the HTTP Request Handler component or the readRawText function until a patch is available

# Example iptables rules to block SSRF to internal ranges
iptables -A OUTPUT -m owner --uid-owner rebuild -d 127.0.0.0/8 -j DROP
iptables -A OUTPUT -m owner --uid-owner rebuild -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -m owner --uid-owner rebuild -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -m owner --uid-owner rebuild -d 192.168.0.0/16 -j DROP
iptables -A OUTPUT -m owner --uid-owner rebuild -d 169.254.169.254 -j DROP