From June to August, part of the McAfee Advanced Threat Research (ATR) team participated in Microsoft’s Azure Sphere Research Challenge. Our research resulted in reporting multiple vulnerabilities classified by Microsoft as “important” or “critical” in the platform that, to date, have qualified for over $160,000 USD in bounty awards scheduled to be contributed to the ACLU ($100,000), St. Jude’s Children’s Research Hospital ($50,000) and PDX Hackerspace (approximately $20,000). With these contributions, we hope to support and give back both to our local hacker community that has really stepped up to help during the COVID crisis, and also recognize, at a larger scale, the importance to protect and further civil liberties and the wellbeing of those most in need.
This blog post is a high–level overview of the program, why we choose to take part in it, and a brief description of our findings. A detailed technical walkthrough of our findings can be found here.
Additionally, Microsoft has released two summary blogs detailing the Azure Sphere Bounty Program as a whole, including McAfee’s efforts and findings. They can be found here:
What is Azure Sphere and the Azure Sphere Research Challenge?
In late May Microsoft started a new bug bounty program for its Azure Sphere platform. Azure Sphere is a hardened IoT device with a secure communication link to the cloud that has been in development for the last few years and reached general availability in early 2020. Microsoft designed and built it from scratch to ensure every aspect of it is as secure as possible, per their security model. To put the theory to test, Microsoft invited a few select partners and hackers to try their best to defeat its security measures.
The Azure sphere team came up with multiple scenarios that would test the security model of the device and qualify for an increased payout from the regular Azure Bug Bounty program. These scenarios range from the ability to bypass certain security measures, to executing code in the hardware enabled secure core of the device.
Research scenarios specific to the Azure Sphere Research Challenge
Why did ATR get involved with the program?
There are multiple reasons why we were keen to participate in this program. First, as security researchers, the Azure Sphere platform is an exciting new research target that has been built from the ground up with security in mind. It showcases what might become of the IoT space in the next few years as legacy platforms are slowly phased out. Being at the forefront of what is being done in the IoT space ensures our research remains current and we are ready to tackle future new challenges. Second, by finding critical bugs in this new platform we help make it more secure and offer our support to make the IoT space increasingly resistant to cyber threats. Finally, as this is a bug bounty program, we decided from the start that we would donate any award we received to charity, thus using our skills to contribute to the social good of our local communities and support causes that transcend the technology sector.
Findings
We’ve reported multiple bugs to Microsoft as a result of our research that were rated Important or Critical:
- Important – Security Feature bypass ($3,300): The inclusion of symlink in application package allows for referencing files outside of the application package mount point.
- Critical – RCE ($48,000): The inclusion of a “character device” in an application package allows for direct interaction with a part of the flash memory, eventually leading to the modification of critical system files and further exploitation.
- Important – EoP ($11,000): Multiple bugs in how uid_map files are processed, allowing for elevation of privilege to the sys user.
- Important – Eop ($11,000): A user with sys privileges can trick Application Manager into unmounting “azcore” and mount a rogue binary in its stead. Triggering a core dump of a running process will then execute the rogue binary with full capabilities & root privileges due to improper handling of permissions in the LSM.
- Critical – EoP ($48,000): Further problems in the privilege dropping of “azcore” leads to the complete bypass of Azure Sphere capability restrictions
- Critical – EoP ($48,000): Due to improper certificate management, it is possible to re-claim a device on the Azure Sphere pre-prod server and obtain a valid capability file that works in the prod environment. This capability file can be used to re-enable application development mode on a finalized device (claimed by a third party). The deployment of the capability file requires physical access to a device.
Conclusion
This research was an exciting opportunity to look at a new platform with very little prior research, while still being in the familiar territory of an ARM device running a hardened Linux operating-system.
Through the bugs we found we were able to get a full chain exploit from a locked device to having root access. However, the Azure Sphere platform has many more security features such as remote attestation, and a hardware enabled secure core that is still holding strong.
Finally, we want to thank Microsoft for the opportunity of participating in this exciting program, and the bounty awards.
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