Critical D-Link Vulnerability Lets Remote Attackers Crash Servers Without Authentication

Security researchers have discovered a critical stack-based buffer overflow vulnerability in D-Link DIR-825 Rev.B 2.10 routers that allows remote attackers to crash servers without requiring authentication.

The vulnerability, designated as CVE-2025-7206, affects the router’s httpd binary and can be exploited by manipulating the language parameter in the switch_language.cgi script.

This flaw poses significant risks to network infrastructure, as attackers can cause denial-of-service conditions by sending specially crafted requests to vulnerable devices.

Vulnerability Details and Technical Analysis

The discovered vulnerability stems from insufficient input validation in the D-Link DIR-825 router’s handling of language parameters.

According to the security researcher known as iC0rner, who reported the flaw, the vulnerability occurs when the language parameter passed through switch_language.cgi is directly stored in nvram persistent storage without proper sanitization.

When the router processes subsequent requests to ASP pages containing specific script tags, the stored language value is retrieved and processed through multiple functions, ultimately leading to a stack overflow condition.

The exploitation process involves a two-step attack sequence. First, attackers send a POST request to the switch_language.cgi endpoint with an excessively long language parameter value.

 This malicious payload gets stored in the router’s non-volatile memory. Subsequently, when any ASP page containing the script tag  is requested, the router attempts to process the stored language value, leading to a stack overflow in the sub_40bFC4 function.

The vulnerability chain begins in the router’s sub_410DDC function, where the language parameter is processed without adequate bounds checking.

The data flows through various parsing functions including do_ebd_js and cmo_get_cfg, eventually reaching the vulnerable sub_40bFC4 function where the overflow occurs.

This results in memory corruption and ultimately causes the httpd service to crash with a segmentation fault.

Proof of Concept and Exploitation Methods

The researcher provided a detailed proof of concept demonstrating the vulnerability’s exploitation.

The attack involves sending a POST request to /switch_language.cgi with a carefully crafted payload containing an extremely long language parameter value.

The payload uses a pattern of repeated characters designed to trigger the buffer overflow condition.

After the malicious language value is stored, accessing any ASP page triggers the vulnerability, causing the httpd service to crash.

This attack vector is particularly concerning because it requires no special privileges or authentication credentials.

The vulnerability can be triggered remotely over the network, making it accessible to both external attackers and malicious insiders with network access.

Security experts recommend immediate implementation of input validation and filtering mechanisms to address this vulnerability.

Organizations using affected D-Link DIR-825 devices should implement network-level protections to restrict access to the management interface and monitor for unusual traffic patterns.

Additionally, firmware updates should be applied as soon as they become available from D-Link.