In 2020, we built-in kCTF into Google’s Vulnerability Rewards Program (VRP) to assist researchers evaluating the safety of Google Kubernetes Engine (GKE) and the underlying Linux kernel. Because the Linux kernel is a key element not only for Google, however for the Web, we began closely investing on this space. We prolonged the VRP’s scope and most reward in 2021 (to $50k), then once more in February 2022 (to $91k), and eventually in August 2022 (to $133k). In 2022, we additionally summarized our learnings up to now in our cookbook, and launched our experimental mitigations for the most typical exploitation strategies.
On this publish, we would prefer to share our learnings and statistics concerning the newest Linux kernel exploit submissions, how efficient our mitigations are towards them, what we do to guard our customers, and, lastly, how we’re altering our program to align incentives to the areas we’re most excited by.
Learnings and Statistics
Since its inception, this system has rewarded researchers with a complete of 1.8 million USD, and prior to now 12 months, there was a transparent pattern: 60% of the submissions exploited the io_uring element of the Linux kernel (we paid out round 1 million USD for io_uring alone). Moreover, io_uring vulnerabilities have been utilized in all of the submissions which bypassed our mitigations.
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Limiting io_uring
To guard our customers, we determined to restrict the utilization of io_uring in Google merchandise:Â
Whereas io_uring brings efficiency advantages, and promptly reacts to safety points with complete safety fixes (like backporting the 5.15 model to the 5.10 secure tree), it’s a pretty new a part of the kernel. As such, io_uring continues to be actively developed, however it’s nonetheless affected by extreme vulnerabilities and likewise gives sturdy exploitation primitives. For these causes, we at the moment think about it protected just for use by trusted elements.
Transparency
At present, we make vulnerability particulars public on our spreadsheet (which now additionally contains CVE particulars), and we have now summarized completely different exploitation strategies in our cookbook. Sooner or later, to make our efforts extra clear and provides sooner suggestions to the neighborhood, we are going to ask researchers to open-source their submissions, together with the code they used.
Introducing kernelCTF
To higher align incentives with our areas of curiosity, we’re shifting our focus from GKE and kCTF to the most recent secure kernel and our mitigations. Because of this, beginning at this time we are going to deal with kernel exploit submissions underneath a brand new title, “kernelCTF,” with its personal reward construction and submission course of. The utmost complete payout for kernelCTF remains to be $133,337 per submission. Whereas the precise GKE kernel configuration remains to be coated by the brand new kernelCTF, exploits affecting non-kernel elements like the complete GKE stack (together with Kubernetes), the container runtime, and GKE itself, are actually individually eligible for vulnerability rewards underneath the kCTF VRP which is returning to its unique reward quantities and circumstances.
Conclusion
Our purpose stays the identical: we’re constructing a pipeline to investigate, experiment, measure, and construct safety mitigations to make the Linux kernel as protected as potential, with the assistance of the safety neighborhood. We hope that over time, we will implement safety mitigations that make it tougher to take advantage of Linux kernel vulnerabilities.
With the title change, we have now moved our communication channel to #kernelctf on Discord, with a separate #kernelctf-announcements channel. Please be part of us there for the most recent updates relating to kernelCTF.
