CVE-2018-3953 : Security Advisory and Response

The Linksys ESeries routers, specifically the Linksys E1200 Firmware Version 2.0.09 and Linksys E2500 Firmware Version 3.0.04, have a vulnerability that allows for OS command injection due to insufficient filtering of data passed to and retrieved from NVRAM.

Understanding CVE-2018-3953

This CVE involves OS command injection vulnerability in Linksys ESeries routers.

What is CVE-2018-3953?

CVE-2018-3953 is an OS command injection vulnerability found in Linksys ESeries routers, specifically affecting the E1200 and E2500 models.

The Impact of CVE-2018-3953

The vulnerability has a CVSS base score of 7.2, indicating a high severity level with significant impacts on confidentiality, integrity, and availability of the affected systems.

Technical Details of CVE-2018-3953

This section provides detailed technical information about the vulnerability.

Vulnerability Description

The vulnerability arises from inadequate data filtering in the 'Router Name' input field, leading to OS command injection. The issue occurs in the apply.cgi script due to the handling of the 'machine_name' POST parameter.

Affected Systems and Versions

Product: Linksys ESeries E1200
Firmware Version: 2.0.09
Product: Linksys ESeries E2500
Firmware Version: 3.0.04

Exploitation Mechanism

Data entered in the 'Router Name' field is used as the 'machine_name' POST parameter in apply.cgi script.
Upon receiving the SIGHUP signal, the 'preinit' binary executes code until reaching offset 0x0042B5C4 in the 'start_lltd' function.
The user-controlled 'machine_name' NVRAM entry value is retrieved using 'nvram_get' and directly inserted into a command for execution.

Mitigation and Prevention

Protecting systems from CVE-2018-3953 requires immediate actions and long-term security practices.

Immediate Steps to Take

Update affected routers to the latest firmware version provided by Linksys.
Implement strong password policies and restrict access to the router's web portal.

Long-Term Security Practices

Regularly monitor and audit network traffic for any suspicious activities.
Conduct security training for users to recognize and report potential security threats.

Patching and Updates

Stay informed about security advisories from Linksys and apply patches promptly to address known vulnerabilities.