Last updated at Wed, 27 Dec 2023 15:14:54 GMT

Rapid7 researcher Arvind Vishwakarma discovered multiple vulnerabilities in the Fortress S03 WiFi Home Security System. These vulnerabilities could result in unauthorized access to control or modify system behavior, and access to unencrypted information in storage or in transit. CVE-2021-39276 describes an instance of CWE-287; specifically, it describes an insecure cloud API deployment which allows unauthenticated users to trivially learn a secret that can then be used to alter the system's functionality remotely. It has an initial CVSS score of 5.3 (medium). CVE-2021-39277 describes an instance of CWE-294, a vulnerability where anyone within Radio Frequency (RF) signal range could capture and replay RF signals to alter systems behavior, and has an initial CVSS score of 5.7.

Product Description

The Fortress S03 WiFi Home Security System is a do it yourself (DIY) consumer grade home security system which leverages WiFi and RF communication to monitor doors, windows, and motion detection to spot possible intruders. Fortress can also electronically monitor the system for you, for a monthly fee. More information about the product can be found at the vendor's website.


These issues were discovered by Rapid7 researcher Arvind Vishwakarma and are being disclosed in accordance with Rapid7's vulnerability disclosure policy.


What follows are details regarding the two disclosed vulnerabilities. Generally speaking, these issues are trivially easy to exploit by motivated attackers who already have some knowledge of the target.

CVE-2021-39276: Unauthenticated API Access

If a malicious actor knows a user’s email address, they can use it to query the cloud-based API to return an International Mobile Equipment Identity (IMEI) number, which appears to also serve as the device's serial number. The following post request structure is used to make this unauthenticated query and return the IMEI:

With a device IMEI number and the user’s email address, it is then possible for a malicious actor to make changes to the system, including disarming its alarm. To disarm the system, the following unauthenticated POST can be sent to the API:

CVE-2021-39277: Vulnerable to RF Signal Replay Attack

The system under test was discovered to be vulnerable to an RF replay attack. When a radio-controlled device has not properly implemented encryption or rotating key protections, this can allow an attacker to capture command-and-control signals over the air and then replay those radio signals in order to perform a function on an associated device.

As a test example, the RF signals used to communicate between the Key Fobs, Door/Window Contact Sensors, and the Fortress Console were identified in the 433 MHz band. Using a software defined radio (SDR) device, the researcher was able to capture normal operations of the device "arm" and "disarm" commands. Then, replaying the captured RF signal communication command would arm and disarm the system without further user interaction.


For CVE-2021-39276, an attacker can use a Fortress S03 user's email address to easily disarm the installed home alarm without the user's knowledge. While this is not usually much of a concern for random, opportunistic home invaders, this is particularly concerning when the attacker already knows the victim well, such as an ex-spouse or other estranged relationship partner.

CVE-2021-39277 presents similar problems but requires less prior knowledge of the victim, as the attacker can simply stake out the property and wait for the victim to use the RF-controlled devices within radio range. The attacker can then replay the "disarm" command later, without the victim's knowledge.


In the absence of a patch or update, to work around the IMEI number exposure described in CVE-2021-39276, users could configure their alarm systems with a unique, one-time email address. Many email systems allow for "plus tagging" an email address. For example, a user could register "" and treat that plus-tagged email address as a stand-in for a password.

For CVE-2021-39277, there seems to be very little a user can do to mitigate the effects of the RF replay issues, absent a firmware update to enforce cryptographic controls on RF signals. Users concerned about this exposure should avoid using key fobs and other RF devices linked to their home security systems.

Disclosure Timeline

  • May, 2021: Issues discovered by Arvind Vishwakarma of Rapid7
  • Thu, May 13, 2021: Initial contact to Fortress support email
  • Thu, May 13, 2021: Ticket #200781 created
  • Mon, May 24, 2021: Ticket #200781 closed by Fortress
  • Wed, Aug 18, 2021: Rapid7 created a follow up ticket, #203001, with vulnerability details and a reiteration of intent to publish
  • Tue, Aug 31, 2021: Published disclosure


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