Security researchers have identified a serious stack-based buffer overflow vulnerability in D-Link DIR-825 routers running firmware version Rev.B 2.10, potentially exposing thousands of home and business networks to remote attacks.
The vulnerability, tracked as CVE-2025-7206, allows attackers to crash router systems without requiring authentication, raising significant concerns about network security.
Critical Security Flaw Discovered in D-Link DIR-825 Router
The vulnerability was discovered by security researcher iC0rner (Mingjie Liang), who found that the router’s web interface improperly handles language parameters submitted through the switch_language.cgi script.
This flaw represents a particularly dangerous type of security weakness because it can be exploited remotely without the attacker needing valid login credentials.
The affected D-Link DIR-825 Rev.B 2.10 firmware contains a critical programming error in its HTTP daemon (httpd) binary.
When processing language settings, the router fails to properly validate the length of user-submitted data, creating an opportunity for malicious actors to overflow the system’s memory stack.
This type of vulnerability is especially concerning because it affects the core networking functionality that millions of users rely on for internet connectivity.
The router’s widespread use in both residential and small business environments makes this discovery particularly significant.
D-Link DIR-825 devices are commonly deployed as primary internet gateways, meaning a successful attack could potentially disconnect entire networks or serve as a launching point for further network infiltration.
Technical Details: How the Attack Works
The vulnerability exploits a weakness in how the router processes language configuration requests.
When an attacker sends an overly long language parameter through the switch_language.cgi interface, the router saves this malicious data directly to its non-volatile RAM (NVRAM) without proper length validation.
The attack unfolds in a two-stage process that demonstrates the sophistication required to exploit modern network devices.
First, the attacker submits a specially crafted POST request to the router’s language switching interface, embedding an extremely long string in the language parameter.
This malicious payload gets stored in the router’s persistent memory without triggering immediate security warnings.
The second stage occurs when any user—including the attacker—requests standard web pages like the login interface.
When the router attempts to load these pages, it processes embedded script tags that reference the stored language setting.
The router’s parsing system then attempts to handle the oversized language parameter, causing it to write beyond the allocated memory boundaries.
This overflow occurs specifically in the router’s sub_40bFC4 function, where the system processes the retrieved language data through multiple variables without implementing proper bounds checking.
The cascading effect ultimately leads to memory corruption and system crashes, effectively creating a denial-of-service condition that can render the router temporarily or permanently inoperable.
Recommended Security Measures and Implications
The discovery highlights critical weaknesses in input validation practices commonly found in consumer networking equipment.
Security experts recommend that D-Link users immediately check their firmware versions and monitor for official security updates from the manufacturer.
Network administrators should implement additional security measures, including strict input validation and filtering for all user-submitted data, as suggested in the vulnerability report.
Organizations using affected D-Link routers should consider implementing network segmentation to limit potential damage from successful exploits.
The vulnerability underscores broader concerns about security practices in the consumer networking industry.
Many router manufacturers continue to ship devices with inadequate input validation, creating opportunities for attackers to exploit fundamental programming errors.
This incident serves as a reminder that even basic network infrastructure requires regular security assessment and updates.
Users should regularly check for firmware updates, use strong administrative passwords, and consider disabling unnecessary web-based management features when possible.
The discovery of CVE-2025-7206 demonstrates that even seemingly minor features like language switching can become significant security vulnerabilities when not properly implemented with appropriate security controls.
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