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April 9, 2025
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How to Fix CVE-2025-31161: Critical Authentication Bypass Vulnerability in CrushFTP Server?
CrushFTP is a popular file transfer server software used by organizations of all sizes. A recently discovered critical vulnerability, CVE-2025-31161, poses a significant threat to CrushFTP servers. This authentication bypass flaw could allow unauthenticated attackers to gain complete control of the affected system.
This article provides security professionals with a comprehensive guide to understand, detect, and remediate CVE-2025-31161. We will delve into the vulnerability's details, its potential impact, and actionable steps to safeguard your CrushFTP server against exploitation. The aim is to equip security professionals with the knowledge to proactively secure their CrushFTP deployments and prevent potential data breaches or system compromises.
A Short Introduction to CrushFTP Server
CrushFTP is a versatile file transfer server that supports various protocols, including FTP, SFTP, WebDAV, HTTP, and HTTPS. It offers features such as user management, access control, automation, and auditing. CrushFTP is often used for secure file sharing, data backup, and workflow automation in various industries. It's commonly deployed as an on-premise solution or within cloud environments.
Summary of the Vulnerability
CVE ID: CVE-2025-31161
Description: Authentication Bypass by Primary Weakness in CrushFTP
CVSS Score: 9.8 (Critical)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVE-2025-31161 is a critical authentication bypass vulnerability affecting CrushFTP versions 10.0.0 to 10.8.3 and 11.0.0 to 11.3.0. The vulnerability lies within the AWS4-HMAC authorization method of the HTTP component of the FTP server. A race condition allows attackers to bypass authentication by manipulating the login process. Specifically, sending a username with a trailing slash (/) triggers an authentication bypass. By providing only the username and a following slash (/), the server will successfully find a username, which triggers the successful anypass authentication process. The server will fail to find the expected SignedHeaders entry, resulting in an index-out-of-bounds error that stops the code from reaching the session cleanup.
Impact of the Vulnerability
Successful exploitation of CVE-2025-31161 can have severe consequences:
An unauthenticated attacker can completely bypass authentication, gaining unauthorized access to the CrushFTP server. This access could elevate privileges to the crushadmin account, granting full administrative control over the system. A compromised CrushFTP server can lead to the unauthorized access, modification, or deletion of sensitive data. Attackers can leverage their control to further compromise the network, potentially planting malware or exfiltrating confidential information. The vulnerability's presence in the CISA Known Exploited Vulnerabilities catalog and the availability of proof-of-concept exploits highlight the urgency of remediation.
Products Affected by the Vulnerability
The following CrushFTP versions are affected by CVE-2025-31161:
| Product | Version(s) Affected |
|---|---|
| CrushFTP v10 | 10.0.0 to 10.8.3 |
| CrushFTP v11 | 11.0.0 to 11.3.0 |
The vulnerability is fixed in:
| Product | Version(s) Fixed |
|---|---|
| CrushFTP v10 | 10.8.4 |
| CrushFTP v11 | 11.3.1 |
How to Check Your Product is Vulnerable?
To determine if your CrushFTP server is vulnerable, follow these steps:
Check the CrushFTP Version: Log in to the CrushFTP administration interface and navigate to the "About" or "System Information" section. Verify the installed version number. If it falls within the affected versions (10.0.0 to 10.8.3 or 11.0.0 to 11.3.0), your server is vulnerable.
Analyze Logs: Examine the CrushFTP server logs for suspicious authentication attempts, especially those involving usernames with trailing slashes. Look for error messages related to the AWS4-HMAC authentication process or index-out-of-bounds errors.
Monitor Network Traffic: Capture and analyze network traffic to the CrushFTP server, looking for HTTP requests with malformed AWS4-HMAC headers or usernames containing trailing slashes.
How to Fix the Vulnerability?
The primary remediation strategy is to upgrade CrushFTP to a patched version.
Upgrade CrushFTP: Upgrade to CrushFTP version 10.8.4 or 11.3.1. These versions contain the necessary patches to address CVE-2025-31161.
Workarounds (if patching is not immediately possible):
Restrict Network Access: Implement network segmentation and firewalls to limit access to the CrushFTP server. Only allow connections from trusted networks.
Monitor Authentication Attempts: Implement robust monitoring and alerting for suspicious authentication attempts, including those with usernames containing trailing slashes.
DMZ Proxy Instance: Utilize a DMZ proxy instance to further isolate the CrushFTP server from direct internet exposure.
Implement Additional Authentication Mechanisms: Consider implementing multi-factor authentication (MFA) to add an additional layer of security.
It's critical to monitor official CrushFTP channels for any further security updates or patches related to this vulnerability.
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Arun KL
Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.
