CVE-2019-20457

Comprehensive Technical Analysis of CVE-2019-20457

1. Vulnerability Assessment and Severity Evaluation

CVE ID: CVE-2019-20457 CVSS Score: 9.1

The vulnerability in Brother MFC-J491DW C1806180757 devices allows an attacker to retrieve the web-interface password hash without authentication. This is due to an incomplete authorization cookie returned in the response header of any failed login attempt. The value of this cookie is the MD5 hash of the password in hexadecimal format. An attacker can derive the true MD5 hash from this incomplete value and use offline cracking attacks to obtain administrative access to the device.

Severity Evaluation:

• CVSS Base Score: 9.1 (Critical)
• Impact: High
• Exploitability: High

The high CVSS score indicates a critical vulnerability that can be easily exploited with severe consequences.

2. Potential Attack Vectors and Exploitation Methods

Attack Vectors:

1. Unauthenticated Access: An attacker can attempt a failed login to retrieve the incomplete authorization cookie.
2. Offline Cracking: Using the incomplete MD5 hash, the attacker can derive the true MD5 hash and perform offline cracking to obtain the actual password.
3. Network Access: The attacker needs network access to the printer's web interface, which can be achieved through local network access or remote access if the printer is exposed to the internet.

Exploitation Methods:

1. Retrieve Incomplete Hash: Perform a failed login attempt to capture the incomplete authorization cookie.
2. Derive True MD5 Hash: Use the incomplete hash to derive the true MD5 hash.
3. Offline Cracking: Use tools like Hashcat or John the Ripper to crack the MD5 hash and obtain the password.
4. Gain Administrative Access: Use the cracked password to log in to the printer's web interface with administrative privileges.

3. Affected Systems and Software Versions

Affected Devices:

• Brother MFC-J491DW C1806180757

Software Versions:

• The vulnerability affects the firmware version running on the specified Brother printer model.

4. Recommended Mitigation Strategies

1. Firmware Update: Apply the latest firmware updates provided by Brother to patch the vulnerability.
2. Network Segmentation: Isolate printers on a separate network segment to limit access.
3. Access Control: Implement strict access controls and restrict administrative access to trusted users only.
4. Monitoring: Enable logging and monitoring of printer access to detect and respond to suspicious activities.
5. Password Management: Use strong, unique passwords for administrative accounts and regularly change them.

5. Impact on Cybersecurity Landscape

This vulnerability highlights the importance of securing IoT devices, including printers, which are often overlooked in cybersecurity strategies. The ease of exploitation and the potential for unauthorized administrative access underscore the need for robust security measures in networked devices. The high CVSS score indicates a significant risk to organizations, particularly those with sensitive information or critical operations that could be disrupted by a compromised printer.

6. Technical Details for Security Professionals

Vulnerability Details:

• Incomplete Authorization Cookie: The response header of a failed login attempt contains an incomplete authorization cookie, which is the MD5 hash of the password in hexadecimal format.
• MD5 Hash Derivation: The incomplete hash can be used to derive the true MD5 hash, which can then be cracked offline.

Exploitation Steps:

1. Capture Incomplete Hash: Use a tool like Burp Suite to capture the response header of a failed login attempt.
2. Derive True MD5 Hash: Use a script or manual method to derive the true MD5 hash from the incomplete value.
3. Offline Cracking: Use a password cracking tool to obtain the actual password from the MD5 hash.
4. Admin Access: Log in to the printer's web interface with the cracked password to gain administrative access.

Mitigation Steps:

1. Firmware Update: Ensure the printer's firmware is up to date with the latest security patches.
2. Network Segmentation: Implement network segmentation to isolate printers from other critical systems.
3. Access Control: Enforce strict access controls and regularly review administrative access.
4. Monitoring: Implement logging and monitoring to detect and respond to unauthorized access attempts.
5. Password Management: Use strong, unique passwords and regularly change them to minimize the risk of password cracking.

By addressing this vulnerability, organizations can enhance their overall cybersecurity posture and protect against potential attacks targeting networked devices.