Google's New Bug Bounties Include Their Custom Linux Kernel's Experimental Security Mitigations

Google uses Linux "in almost everything," according to the leader of Google's "product security response" team - including Chromebooks, Android smartphones, and even Google Cloud. "Because of this, we have heavily invested in Linux's security - and today, we're announcing how we're building on those investments and increasing our rewards."In 2020, we launched an open-source Kubernetes-based Capture-the-Flag (CTF) project called, kCTF. The kCTF Vulnerability Rewards Program lets researchers connect to our Google Kubernetes Engine (GKE) instances, and if they can hack it, they get a flag, and are potentially rewarded. All of GKE and its dependencies are in scope, but every flag caught so far has been a container breakout through a Linux kernel vulnerability. We've learned that finding and exploiting heap memory corruption vulnerabilities in the Linux kernel could be made a lot harder. Unfortunately, security mitigations are often hard to quantify, however, we think we've found a way to do so concretely going forward.... First, we are indefinitely extending the increased reward amounts we announced earlier this year, meaning we'll continue to pay $20,000 - $91,337 USD for vulnerabilities on our lab kCTF deployment to reward the important work being done to understand and improve kernel security. This is in addition to our existing patch rewards for proactive security improvements. Second, we're launching new instances with additional rewards to evaluate the latest Linux kernel stable image as well as new experimental mitigations in a custom kernel we've built. Rather than simply learning about the current state of the stable kernels, the new instances will be used to ask the community to help us evaluate the value of both our latest and more experimental security mitigations. Today, we are starting with a set of mitigations we believe will make most of the vulnerabilities (9/10 vulns and 10/13 exploits) we received this past year more difficult to exploit. For new exploits of vulnerabilities submitted which also compromise the latest Linux kernel, we will pay an additional $21,000 USD. For those which compromise our custom Linux kernel with our experimental mitigations, the reward will be another $21,000 USD (if they are clearly bypassing the mitigations we are testing). This brings the total rewards up to a maximum of $133,337 USD. We hope this will allow us to learn more about how hard (or easy) it is to bypass our experimental mitigations..... With the kCTF VRP program, we are building a pipeline to analyze, experiment, measure and build security mitigations to make the Linux kernel as safe as we can with the help of the security community. We hope that, over time, we will be able to make security mitigations that make exploitation of Linux kernel vulnerabilities as hard as possible. "We don't care about vulnerabilities; we care about exploits," Vela told the Register. "We expect the vulnerabilities are there, they will get patched, and that's nice and all. But the whole idea is what do to beyond just patching a couple of vulnerabilities."In total, Google paid out $8.7 million in rewards to almost 700 researchers across its various VPRs last year. "We are just one actor in the whole community that happens to have economic resources, financial resources, but we need the community to help us make the Kernel better," Vela said. "If the community is engaged and helps us validate the mitigations that we have, then, we will continue growing on top of that. But the whole idea is that we need to see where the community wants us to go with this...." [I]t's not always about the cash payout, according to Vela, and different bug hunters have different motivations. Some want money, some want fame and some just want to solve an interesting problem, Vela said. "We are trying to find the right combination to captivate people."

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