**Summary: Unauthenticated Remote Code Execution Vulnerability in INSTAR 2K+ and 4K Series IP Cameras**
In this technical deep dive, Michael Imfeld details his journey uncovering and exploiting a critical vulnerability in the INSTAR IN-8401 2K+ IP camera, a modern Internet of Things (IoT) device used for surveillance. His research highlights not only the process of extracting and analyzing firmware but also demonstrates how a previously unknown flaw in the camera’s software can be exploited to gain unauthenticated remote code execution (RCE)—a severe security risk for thousands of devices exposed online.
**Background and Motivation**
Following earlier work on ARM exploitation, Imfeld sought a more challenging target: a contemporary IoT device with a broader attack surface. He selected the IN-8401 2K+, which shares its firmware across INSTAR's 2K+ and 4K product lines. According to data from Shodan, there are about 12,000 such devices accessible from the public internet, amplifying the impact of any security issue found.
**Firmware Extraction and Device Access**
The first step in vulnerability research is gaining access to the device’s firmware, which contains the binaries, configuration files, and scripts necessary for both static and dynamic analysis. Imfeld began by reviewing INSTAR’s documentation and discovered that, although official instructions for recovering from a failed firmware upgrade were written for older models, the process might still apply due to component reuse across product lines.
By opening the camera enclosure, Imfeld identified the hardware debugging interface (UART). He connected this to his Linux machine using an FTDI USB-to-serial converter, which allowed him to interact with the device’s boot process. While the documentation suggested it was possible to obtain a root shell by interrupting the boot, the actual result was access to the U-Boot bootloader, not the full operating system. However, by modifying the kernel boot parameters to start a shell (`init=/bin/sh`), he circumvented this limitation, created a new root user, and successfully extracted the device’s entire filesystem for offline analysis.
**Mapping the Attack Surface**
With the firmware in hand, Imfeld examined the device’s web stack, focusing on components reachable without authentication. Notably, a lighttpd web server acts as a reverse proxy, directing requests for `.cgi` files to a backend binary called `fcgi_server`. Another process, `ipc_server`, is involved in handling authentication and core application logic, receiving requests via a custom serialized protocol between the two backends.
These two binaries—`fcgi_server` and `ipc_server`—were identified as prime targets for further analysis, since they could both be reached by unauthenticated users.
**Hunting for Vulnerabilities**
Imfeld’s approach combined fuzzing, static analysis, and dynamic testing. While initial black-box fuzzing using the boofuzz framework resulted in the discovery of a crash (later assigned CVE-2025-