CVE-2025-29514: D-Link DSL-7740C Auth Bypass Vulnerability

CVE-2025-29514 Overview

CVE-2025-29514 is a critical incorrect access control vulnerability affecting D-Link DSL-7740C routers with firmware version DSL7740C.V6.TR069.20211230. The vulnerability exists in the config.xgi function, which fails to properly validate user authentication before processing configuration file download requests. This allows unauthenticated remote attackers to download the device's configuration file by sending a specially crafted web request, potentially exposing sensitive network credentials, administrative passwords, and infrastructure details.

Critical Impact

Unauthenticated attackers can remotely download the complete device configuration, exposing administrative credentials, network topology, and security settings without any authentication requirements.

Affected Products

• D-Link DSL-7740C with firmware version 6.TR069.20211230
• D-Link DSL-7740C hardware devices
• D-Link DSL-7740C Firmware

Discovery Timeline

• 2025-08-25 - CVE-2025-29514 published to NVD
• 2025-09-02 - Last updated in NVD database

Technical Details for CVE-2025-29514

Vulnerability Analysis

This vulnerability stems from improper access control (CWE-284) in the web management interface of D-Link DSL-7740C routers. The config.xgi function, which handles configuration file operations, does not properly enforce authentication checks before serving the device configuration file to requesting clients. As a network-accessible vulnerability requiring no authentication or user interaction, attackers can exploit this flaw remotely to obtain the complete router configuration, including stored credentials, wireless security keys, and network topology information.

Root Cause

The root cause is a broken access control mechanism in the config.xgi web handler function. The firmware fails to verify that incoming requests for configuration file downloads originate from authenticated administrative sessions. This design flaw allows any network-accessible attacker to bypass authentication entirely and directly request sensitive configuration data through a crafted HTTP request.

Attack Vector

The attack exploits the network-accessible web management interface of the D-Link DSL-7740C. An attacker can craft a malicious HTTP request targeting the config.xgi endpoint to trigger the configuration file download without providing any authentication credentials. The attack requires network access to the device's management interface but requires no privileges, user interaction, or special conditions.

The vulnerability allows attackers to retrieve sensitive configuration data including administrative passwords, wireless security keys, ISP credentials, and network routing information by sending crafted requests to the vulnerable endpoint. Detailed proof-of-concept information is available in the GitHub Gist PoC Code published by the security researcher.

Detection Methods for CVE-2025-29514

Indicators of Compromise

• Unexpected HTTP requests to the config.xgi endpoint from external or unauthorized IP addresses
• Anomalous downloads of configuration files from the router's web management interface
• Authentication logs showing configuration access without corresponding successful login events
• Network traffic analysis revealing configuration file data being transmitted to unknown destinations

Detection Strategies

• Monitor web server access logs for requests containing config.xgi in the request path
• Implement network-based intrusion detection rules to alert on configuration file download patterns from the router
• Deploy SentinelOne Singularity to detect anomalous network behavior patterns associated with configuration exfiltration
• Establish baseline traffic patterns for router management interfaces and alert on deviations

Monitoring Recommendations

• Enable verbose logging on the D-Link DSL-7740C web management interface if supported
• Deploy network monitoring solutions to capture and analyze traffic to/from router management ports
• Implement alerting for any access to sensitive configuration endpoints from non-administrative networks
• Review router access logs regularly for signs of unauthorized configuration access attempts

How to Mitigate CVE-2025-29514

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Implement firewall rules to block external access to the router's management ports (typically port 80/443)
• Change all administrative credentials and wireless security keys as a precaution, as they may have already been compromised
• Consider network segmentation to isolate vulnerable devices from critical infrastructure

Patch Information

D-Link has not released a specific patch addressing this vulnerability at the time of publication. Organizations should consult the D-Link Security Bulletin for firmware updates and security advisories. Given the end-of-life status of many D-Link consumer devices, affected organizations should evaluate whether replacement with actively supported hardware is necessary.

Workarounds

• Disable remote management access to the router's web interface entirely
• Implement ACLs or firewall rules to restrict management interface access to specific trusted IP addresses only
• Place the router behind an additional firewall or security appliance that can filter malicious requests
• Consider replacing the affected device with a currently supported router model that receives active security updates
• If replacement is not immediately possible, monitor for unauthorized access attempts while planning for device replacement

# Example firewall rules to restrict management interface access
# Allow management access only from trusted admin subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
# Block all other access to management ports
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP