A serious buffer overflow flaw in the firmware of the D-Link DIR-825 Rev.B router version 2.10 allows remote attackers without authentication and without any interaction with the user (zero-click) to cause the device's HTTP server to crash .
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The issue is tracked as CVE-2025-7206 and is located in the router's httpd executable. It results from incorrect handling of the language in the endpoint switch_language.cgi.
Exploiting the D-Link flaw does not require valid credentials or user interaction, meaning an attacker only needs access to the device's administrative environment over the network to cause a denial of service (DoS). According to security researcher iC0rner , the flaw is located in the sub_410DDC function of the httpd executable, which directly accepts attacker-controlled data without length checking.
Specifically, when an HTTP POST is made to switch_language.cgi, the language is permanently stored in NVRAM.
This happens before any data validation or sanitization, meaning that a maliciously large string can cause a local stack frame overflow. Once the overflowed entry is stored in NVRAM, any subsequent request to an ASP page in the admin interface (e.g. login.asp) triggers the dynamic loading of the corresponding JavaScript for the language.
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When parsing this file, the HTTP server (httpd) follows the do_ebd_js, ultimately ending up calling nvram_get(“language”).
The returned string is passed through a complex chain of internal functions—such as sub_40BFC4—where another unsafe data concatenation is performed, which writes beyond the bounds of the specified buffer, ultimately causing a segmentation fault and a service.
Organizations relying on the D-Link DIR-825 Rev.B version 2.10 router for functions such as VPN termination , guest networks, or IoT device isolation should consider the following risk mitigation measures:
- Installation of Updated Firmware (Firmware Update)
- Network Access Control (Network Access Controls)
- Enable Intrusion Detection System (Intrusion Detection)
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By implementing these measures, administrators can protect themselves from the D-Link CVE-2025-7206 flaw and enhance confidence in the security of their network perimeter.
Source: cybersecuritynews
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