CVE-2023-43177: CrushFTP Privilege Escalation Flaw

CVE-2023-43177 Overview

CVE-2023-43177 is a critical vulnerability affecting CrushFTP prior to version 10.5.1. The vulnerability involves Improperly Controlled Modification of Dynamically-Determined Object Attributes (CWE-913), which allows unauthenticated attackers to manipulate object properties at runtime. This type of vulnerability can lead to severe security implications including unauthorized access, data manipulation, and potential remote code execution.

Critical Impact

This vulnerability allows unauthenticated remote attackers to exploit the mass assignment flaw in CrushFTP, potentially leading to complete system compromise including data exfiltration, unauthorized administrative access, and remote code execution.

Affected Products

• CrushFTP versions prior to 10.5.1
• All CrushFTP deployments using vulnerable configurations
• Enterprise file transfer environments running unpatched CrushFTP instances

Discovery Timeline

• 2023-11-18 - CVE-2023-43177 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-43177

Vulnerability Analysis

This vulnerability falls under CWE-913 (Improperly Controlled Modification of Dynamically-Determined Object Attributes), commonly known as a mass assignment or object injection vulnerability. The flaw exists in how CrushFTP processes user-supplied input when modifying object attributes dynamically at runtime.

In vulnerable configurations, CrushFTP fails to properly validate and restrict which object properties can be modified through external input. This allows attackers to inject or modify arbitrary object attributes that should be protected from user manipulation. The network-accessible nature of CrushFTP deployments makes this vulnerability particularly dangerous as it can be exploited remotely without authentication.

The vulnerability has an extremely high exploitation probability, placing it in the top percentile of vulnerabilities likely to be exploited in the wild. Organizations using CrushFTP for file transfer operations should treat this as a high-priority remediation target.

Root Cause

The root cause of CVE-2023-43177 lies in insufficient input validation and improper access controls on dynamically-determined object attributes within CrushFTP. When processing requests, the application fails to implement proper allowlists or blocklists for object properties that can be modified through user input.

This design flaw allows attackers to bind arbitrary parameters to internal objects, potentially overwriting security-critical attributes such as authentication tokens, access control flags, or session identifiers. The absence of proper attribute filtering enables mass assignment attacks where malicious input can modify protected application state.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no prior authentication or user interaction. An attacker can craft malicious requests targeting the CrushFTP server to exploit the mass assignment flaw.

The exploitation process typically involves identifying object endpoints that accept user-controlled input and probing for modifiable attributes that influence application behavior or security controls. By manipulating these attributes, attackers can escalate privileges, bypass authentication mechanisms, or gain unauthorized access to sensitive functionality.

Detailed technical analysis and proof-of-concept information can be found in the ConvergeTP Zero-Day Disclosure and the GitHub CVE Disclosure Document.

Detection Methods for CVE-2023-43177

Indicators of Compromise

• Unusual HTTP requests containing unexpected parameter names or object attribute manipulations targeting CrushFTP endpoints
• Authentication bypass events or unauthorized administrative access without valid credentials
• Anomalous modifications to user accounts, permissions, or session data in CrushFTP logs
• Unexpected changes to server configuration or file system access patterns

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests with suspicious parameter injection patterns
• Monitor CrushFTP application logs for authentication anomalies and unexpected privilege changes
• Deploy network intrusion detection signatures targeting known CrushFTP exploitation patterns
• Enable verbose logging on CrushFTP servers to capture detailed request information for forensic analysis

Monitoring Recommendations

• Configure SIEM alerts for unusual CrushFTP authentication patterns or access from unexpected geographic locations
• Monitor for bulk file access or data exfiltration patterns that may indicate post-exploitation activity
• Implement file integrity monitoring on CrushFTP configuration files and system binaries
• Review CrushFTP audit logs regularly for unauthorized administrative actions

How to Mitigate CVE-2023-43177

Immediate Actions Required

• Upgrade CrushFTP to version 10.5.1 or later immediately to address this vulnerability
• Implement network segmentation to limit exposure of CrushFTP servers to untrusted networks
• Enable additional authentication mechanisms such as multi-factor authentication where supported
• Review and audit existing CrushFTP user accounts and permissions for any signs of compromise

Patch Information

CrushFTP has addressed this vulnerability in version 10.5.1. Organizations should download and apply the latest security update from the official CrushFTP distribution channels. Prior to upgrading, ensure backups of current configurations and data are completed.

After patching, administrators should verify the upgrade was successful and review any security configurations that may need adjustment. The vendor-provided update resolves the improper input validation that allowed mass assignment attacks.

Workarounds

• Place CrushFTP servers behind a reverse proxy with strict input filtering to limit parameter manipulation
• Implement IP-based access controls to restrict CrushFTP access to known trusted networks
• Disable unnecessary features and endpoints in CrushFTP to reduce the attack surface
• Monitor and rate-limit requests to CrushFTP to detect and slow down exploitation attempts

# Example firewall configuration to restrict CrushFTP access
# Limit access to CrushFTP ports to trusted networks only
iptables -A INPUT -p tcp --dport 21 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 21 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP