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In 2020, we built-in kCTF into Google’s Vulnerability Rewards Program (VRP) to help researchers evaluating the safety of Google Kubernetes Engine (GKE) and the underlying Linux kernel. Because the Linux kernel is a key part 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 thus far 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 in opposition to 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 occupied with.Learnings and StatisticsSince 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 development: 60% of the submissions exploited the io_uring part of the Linux kernel (we paid out round 1 million USD for io_uring alone). Moreover, io_uring vulnerabilities had been utilized in all of the submissions which bypassed our mitigations. Limiting io_uringTo shield our customers, we determined to restrict the utilization of io_uring in Google merchandise: 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 steady 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 supplies sturdy exploitation primitives. For these causes, we presently contemplate it protected just for use by trusted parts.TransparencyCurrently, we make vulnerability particulars public on our spreadsheet (which now additionally consists of CVE particulars), and we’ve summarized totally different exploitation strategies in our cookbook. Sooner or later, to make our efforts extra clear and provides quicker suggestions to the group, we’ll ask researchers to open-source their submissions, together with the code they used.Introducing kernelCTFTo higher align incentives with our areas of curiosity, we’re shifting our focus from GKE and kCTF to the newest steady kernel and our mitigations. Consequently, beginning immediately we’ll deal with kernel exploit submissions below a brand new title, “kernelCTF,” with its personal reward construction and submission course of. The utmost whole payout for kernelCTF continues to be $133,337 per submission. Whereas the particular GKE kernel configuration continues to be coated by the brand new kernelCTF, exploits affecting non-kernel parts like the complete GKE stack (together with Kubernetes), the container runtime, and GKE itself, are actually individually eligible for vulnerability rewards below the kCTF VRP which is returning to its unique reward quantities and situations.ConclusionOur 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 doable, with the assistance of the safety group. We hope that over time, we will implement safety mitigations that make it harder to take advantage of Linux kernel vulnerabilities.With the title change, we’ve moved our communication channel to #kernelctf on Discord, with a separate #kernelctf-announcements channel. Please be a part of us there for the newest updates relating to kernelCTF.
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