A critical security flaw has been identified in D-Link’s DIR-825 Rev.B 2.10 router firmware, allowing unauthenticated remote attackers to crash the device’s HTTP server without any user interaction. This zero-click vulnerability, designated as CVE-2025-7206, poses a significant risk to network stability and security.
Understanding CVE-2025-7206
The vulnerability resides in the router’s HTTP daemon (httpd) binary, specifically within the `switch_language.cgi` endpoint. The flaw stems from improper handling of the `language` parameter, which, when exploited, can lead to a stack-based buffer overflow. This occurs because the input is stored in the router’s Non-Volatile Random-Access Memory (NVRAM) without adequate length checks, allowing an attacker to overwrite critical memory regions.
Exploitation Mechanics
Exploiting this vulnerability requires no authentication or user interaction. An attacker with network access to the router’s management interface can send a specially crafted HTTP POST request to the `switch_language.cgi` endpoint with an oversized `language` parameter. This malicious input is then stored in NVRAM. Subsequent requests to any ASP page, such as `login.asp`, trigger the router to load the corrupted language setting, leading to a buffer overflow and crashing the HTTP server.
Potential Impact
The exploitation of CVE-2025-7206 can result in a denial-of-service (DoS) condition, disrupting various network services. This includes:
– VPN Services: Remote workers relying on VPN connections may experience interruptions, affecting productivity and secure access to internal resources.
– Guest Wi-Fi Networks: Public or guest Wi-Fi services provided by businesses could become unavailable, impacting customer satisfaction and operations.
– IoT Device Management: Smart devices connected to the network may lose connectivity or functionality, leading to potential operational issues.
Proof-of-Concept Demonstration
Security researcher iC0rner has provided a proof-of-concept (PoC) to demonstrate the exploit:
1. Setting the Malicious Parameter:
“`http
POST /switch_language.cgi HTTP/1.1
Host: [Router_IP]
Content-Type: application/x-www-form-urlencoded
Content-Length: [Length]
language=[Oversized_String]
“`
2. Triggering the Crash:
“`http
GET /login.asp HTTP/1.1
Host: [Router_IP]
“`
In this PoC, `[Router_IP]` represents the IP address of the target router, and `[Oversized_String]` is a string long enough to cause the buffer overflow. Upon execution, the router’s HTTP server crashes, demonstrating the ease with which this vulnerability can be exploited.
Mitigation Strategies
To protect against potential exploitation of CVE-2025-7206, the following measures are recommended:
1. Firmware Update: D-Link should release a firmware update addressing this vulnerability by implementing proper input validation and bounds checking. Users are advised to apply this update as soon as it becomes available.
2. Restrict Management Interface Access: Limit access to the router’s web management interface by configuring firewall rules to allow only trusted IP addresses. This reduces the attack surface by preventing unauthorized network access.
3. Monitor Network Traffic: Implement intrusion detection systems (IDS) to monitor for unusual HTTP POST requests to `switch_language.cgi` with excessively long `language` parameters. Such monitoring can help identify and block potential exploitation attempts.
4. Disable Unnecessary Services: If the language switching feature is not essential, consider disabling it to eliminate the attack vector associated with this vulnerability.
Broader Implications
This vulnerability highlights the critical importance of robust input validation and secure coding practices in network devices. Manufacturers must prioritize security throughout the product lifecycle, including post-release support and timely updates for identified vulnerabilities.
Conclusion
CVE-2025-7206 presents a significant security risk to networks utilizing D-Link DIR-825 Rev.B 2.10 routers. Immediate action is required to mitigate potential exploitation. Users should stay informed about firmware updates from D-Link and implement the recommended security measures to safeguard their networks against this and similar vulnerabilities.
