FileCodeBox Rate Limit Bypass: CVE-2025-51663 Exposes Systems to DoS and Brute-Force Attacks

Overview

CVE-2025-51663 details a security vulnerability within the IPRateLimit implementation of FileCodeBox versions up to 2.2. This vulnerability allows remote attackers to circumvent IP-based rate limiting and failed attempt restrictions by manipulating HTTP headers, specifically X-Real-IP and X-Forwarded-For. Successful exploitation can lead to Denial-of-Service (DoS) attacks or brute-force attempts against share codes.

Technical Details

The FileCodeBox application utilizes IP-based rate limiting to protect against abuse and unauthorized access. However, the implementation trusts the X-Real-IP and X-Forwarded-For HTTP headers to identify client IP addresses. Attackers can forge these headers with arbitrary values, effectively bypassing the rate limit mechanism. By sending requests with different spoofed IP addresses, an attacker can exceed the intended rate limits without being blocked, thereby performing DoS attacks. Furthermore, this bypass enables brute-force attacks targeting share codes, as the attacker can attempt numerous combinations from a seemingly diverse set of IP addresses.

CVSS Analysis

Currently, the CVE record indicates that a CVSS score is not available (N/A). This may be because the vulnerability is newly discovered or is still under assessment. However, given the potential for DoS and brute-force attacks, it’s crucial to address this vulnerability promptly. Once assigned, the CVSS score will provide a more accurate measure of the severity of the vulnerability.

Possible Impact

The exploitation of CVE-2025-51663 can have significant consequences:

• Denial of Service (DoS): Attackers can overwhelm the FileCodeBox server with excessive requests, rendering it unavailable to legitimate users.
• Brute-Force Attacks: Attackers can attempt to guess share codes, potentially gaining unauthorized access to sensitive files.
• Resource Exhaustion: Continued exploitation can lead to resource exhaustion on the server, impacting overall system performance.

Mitigation and Patch Steps

To mitigate the risk posed by CVE-2025-51663, consider the following steps:

1. Upgrade FileCodeBox: Check for and apply any available patches or upgrades released by the FileCodeBox developers (vastsa). This is the most effective way to address the vulnerability.
2. Validate and Sanitize IP Addresses: If an upgrade is not immediately possible, implement server-side validation and sanitization of the X-Real-IP and X-Forwarded-For headers. Exercise extreme caution when relying on these headers, as they can be easily spoofed.
3. Implement Reverse Proxy Configuration: Configure your reverse proxy (e.g., Nginx, Apache) to only accept X-Real-IP and X-Forwarded-For headers from trusted sources (e.g., internal network). Discard or sanitize headers from untrusted sources.
4. Web Application Firewall (WAF): Deploy a WAF to detect and block malicious requests attempting to exploit the vulnerability. Configure the WAF to look for suspicious patterns in the X-Real-IP and X-Forwarded-For headers.
5. Rate Limiting at Reverse Proxy: Implement rate limiting at the reverse proxy level, independent of the application’s rate limiting. This provides an additional layer of protection.

References

• FileCodeBox GitHub Repository
• FileCodeBox Issue #350