Description

A vulnerability was determined in D-Link DIR-868L 2.01b05. This issue affects the function strcpy of the file /webfa_authentication.cgi of the component Authentication Handler. Executing a manipulation of the argument id/password can lead to stack-based buffer overflow. The attack can be executed remotely. The exploit has been publicly disclosed and may be utilized.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "10.0",
  "pubDate": "2026-09-20T21:16:55.780Z",
  "pubdate": "2026-09-20T21:16:55.780Z",
  "executiveSummary": "A critical stack-based buffer overflow vulnerability exists in the D-Link DIR-868L, version 2.01b05. The flaw resides within the Authentication Handler component, specifically within the /webfa_authentication.cgi file.\nThe vulnerability is triggered by improper boundary checking when processing the 'id' or 'password' arguments provided during the authentication process. Because the application uses the vulnerable strcpy function to copy user-supplied input into a fixed-length stack buffer without validating the length of the data, an attacker can supply an excessively long string to overwrite adjacent memory, including the return address on the stack.\nThis vulnerability is remotely exploitable, allowing unauthenticated attackers to execute arbitrary code or cause a denial-of-service condition on the affected router. Given the public disclosure of exploit material, the risk to operational security is high, as the flaw can be leveraged to gain unauthorized remote control over the device. Immediate mitigation or device replacement is recommended for exposed systems.",
  "technicalDetails": "The root cause of this vulnerability is the use of the inherently unsafe strcpy function within the Authentication Handler of the D-Link DIR-868L, version 2.01b05. Specifically, the function processes user-supplied authentication parameters—namely the 'id' and 'password' fields—passed to the /webfa_authentication.cgi file.\nIn a secure implementation, inputs are validated against fixed buffer sizes before memory operations occur. However, in this instance, the /webfa_authentication.cgi component fails to implement length constraints. When an attacker sends a malicious HTTP request containing an 'id' or 'password' argument that exceeds the allocated capacity of the destination stack buffer, the strcpy function continues copying data beyond the buffer's intended boundary. This action results in a stack-based buffer overflow.\nThe attack flow proceeds as follows: An attacker sends a crafted remote request to the vulnerable endpoint /webfa_authentication.cgi. This request includes an 'id' or 'password' parameter filled with a carefully constructed payload. This payload typically contains a large sequence of characters intended to fill the buffer, followed by a memory address designed to overwrite the function's return address stored on the stack. When the function completes execution, the instruction pointer is redirected to the attacker-controlled address. If shellcode is included in the payload, the CPU execution flow is diverted to the injected malicious code.\nBecause the vulnerable function executes as part of the authentication process, the exploit does not require prior valid credentials, allowing unauthenticated remote attackers to target the device directly over the network. The post-exploitation impact is severe, potentially granting the attacker complete control over the device with the privileges of the web server process. This can lead to persistent backdoor installation, configuration modification, or full compromise of the router’s operational integrity. The nature of this vulnerability is a classic stack overflow, common in firmware where legacy C library functions like strcpy are utilized without adequate input sanitization."
}