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

CVE-2025-29514 Overview

CVE-2025-29514 is an incorrect access control vulnerability in the config.xgi function of the D-Link DSL-7740C router running firmware DSL7740C.V6.TR069.20211230. Unauthenticated attackers can download the device configuration file by sending a crafted web request to the affected endpoint. The configuration file typically contains sensitive data including administrative credentials, network settings, and ISP provisioning parameters. The flaw is classified under [CWE-284] (Improper Access Control) and carries network-based exploitability with no authentication or user interaction required.

Critical Impact

Remote unauthenticated attackers can exfiltrate the full router configuration, exposing administrative credentials and enabling full device takeover.

Affected Products

• D-Link DSL-7740C router hardware
• D-Link DSL-7740C firmware version DSL7740C.V6.TR069.20211230
• Deployments exposing the router web management interface to untrusted networks

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

The vulnerability resides in the config.xgi handler exposed by the D-Link DSL-7740C web management interface. This endpoint serves configuration export functionality but fails to enforce authentication or authorization checks on incoming requests. An attacker who can reach the device over the network can issue an HTTP request to config.xgi and receive the router configuration file in response.

The configuration file in DSL-class CPE devices commonly contains administrative usernames and password hashes, PPPoE ISP credentials, Wi-Fi pre-shared keys, TR-069 ACS URLs and credentials, SNMP community strings, and remote management settings. Disclosure of this data enables full administrative compromise of the router and pivoting into the connected network.

Root Cause

The root cause is missing access control enforcement on a sensitive web endpoint. The config.xgi function does not validate session tokens, authentication cookies, or source restrictions before returning configuration data. This is a classic [CWE-284] flaw where a privileged operation is reachable by any caller.

Attack Vector

Exploitation requires only network reachability to the router's HTTP management interface. The attacker sends a crafted GET or POST request to the config.xgi endpoint and the device returns the configuration file without prompting for credentials. Where ISPs or users expose the web UI to the WAN interface, the attack is reachable from the public internet. On LAN-only deployments, any device on the local network, including a compromised IoT endpoint or guest device, can retrieve the configuration. A public proof-of-concept is referenced via a GitHub Gist PoC.

No verified exploit code is reproduced here. Refer to the linked
GitHub Gist for the published proof-of-concept request format.

Detection Methods for CVE-2025-29514

Indicators of Compromise

• HTTP requests to the /config.xgi URI path on DSL-7740C devices originating from unexpected source addresses
• Outbound transfer of configuration file content from the router immediately following an unauthenticated HTTP request
• Unexpected administrative logins to the router shortly after config.xgi access events
• Modifications to DNS, DHCP, or remote management settings without a corresponding authenticated admin session

Detection Strategies

• Inspect web server and firewall logs for any GET or POST requests targeting config.xgi on D-Link DSL-7740C devices
• Alert on requests to router management endpoints that lack a preceding authenticated session cookie
• Correlate router configuration retrieval events with subsequent credential reuse against other internal systems

Monitoring Recommendations

• Forward router HTTP and syslog events to a centralized log platform for retention and anomaly analysis
• Monitor for WAN-side access attempts to the router management interface and block them at the network edge
• Track outbound bandwidth from the router for anomalous transfer sizes consistent with configuration exfiltration

How to Mitigate CVE-2025-29514

Immediate Actions Required

• Disable remote (WAN-side) web management on the DSL-7740C until a vendor patch is verified and applied
• Restrict LAN access to the router management interface to a dedicated administrative VLAN or host
• Rotate all credentials stored on the device, including admin passwords, Wi-Fi PSKs, PPPoE, and TR-069 ACS credentials
• Review the router configuration for unauthorized changes to DNS servers, port forwards, and remote management settings

Patch Information

No fixed firmware version is referenced in the NVD entry at the time of publication. Administrators should monitor the D-Link Security Bulletin for an updated firmware release addressing CVE-2025-29514 and apply it as soon as it is available. The DSL-7740C is a regional product line; replacement with a supported model may be required if no patch is released.

Workarounds

• Block inbound TCP traffic to the router's HTTP and HTTPS management ports from the WAN interface
• Place the device behind an upstream firewall that restricts management plane access to trusted IP ranges
• Segment the router from sensitive internal networks so a configuration disclosure does not expose downstream credentials
• Consider replacing the affected DSL-7740C with a currently supported model if a fix is not made available by the vendor

# Example: block WAN-side access to router management ports at an upstream firewall
iptables -I FORWARD -d <router-wan-ip> -p tcp -m multiport --dports 80,443,8080 -j DROP