Making Linux Kernel Exploit Cooking Tougher

The Linux kernel is a key part for the safety of the Web. Google makes use of Linux in nearly every little thing, from the computer systems our workers use, to the merchandise individuals all over the world use every day like Chromebooks, Android on telephones, automobiles, and TVs, and workloads on Google Cloud. Due to this, we have now closely invested in Linux’s safety – and immediately, we’re asserting how we’re constructing on these investments and rising our rewards.

In 2020, we launched an open-source Kubernetes-based Seize-the-Flag (CTF) mission known as, kCTF. The kCTF Vulnerability Rewards Program (VRP) lets researchers hook up with our Google Kubernetes Engine (GKE) cases, and if they’ll hack it, they get a flag, and are doubtlessly rewarded. All of GKE and its dependencies are in scope, however each flag caught up to now has been a container breakout by a Linux kernel vulnerability. We’ve discovered that discovering and exploiting heap reminiscence corruption vulnerabilities within the Linux kernel may very well be made quite a bit more durable. Sadly, safety mitigations are sometimes exhausting to quantify, nevertheless, we expect we’ve discovered a method to take action concretely going ahead.

Once we launched kCTF, we hoped to construct a group of Linux kernel exploitation hackers. This labored nicely and allowed the group to be taught from a number of members of the safety group like Markak, starlabs, Crusaders of Rust, d3v17, slipper@pangu, valis, kylebot, pqlqpql and Awarau.

Now, we’re making updates to the kCTF program. First, we’re indefinitely extending the elevated reward quantities we introduced earlier this 12 months, which means we’ll proceed to pay $20,000 – $91,337 USD for vulnerabilities on our lab kCTF deployment to reward the vital work being carried out to grasp and enhance kernel safety. That is along with our present patch rewards for proactive safety enhancements.

Second, we’re launching new cases with further rewards to guage the most recent Linux kernel secure picture in addition to new experimental mitigations in a customized kernel we have constructed. Somewhat than merely studying in regards to the present state of the secure kernels, the brand new cases will likely be used to ask the group to assist us consider the worth of each our newest and extra experimental safety mitigations. 

Immediately, we’re beginning with a set of mitigations we consider will make many of the vulnerabilities (9/10 vulns and 10/13 exploits) we obtained this previous 12 months harder to take advantage of. For brand spanking new exploits of vulnerabilities submitted which additionally compromise the most recent Linux kernel, we can pay an extra $21,000 USD. For these which compromise our customized Linux kernel with our experimental mitigations, the reward will likely be one other $21,000 USD (if they’re clearly bypassing the mitigations we’re testing). This brings the overall rewards as much as a most of $133,337 USD. We hope this may enable us to be taught extra about how exhausting (or simple) it’s to bypass our experimental mitigations.

The mitigations we have constructed try and deal with the next exploit primitives:

With the kCTF VRP program, we’re constructing a pipeline to investigate, experiment, measure and construct safety mitigations to make the Linux kernel as protected as we will with the assistance of the safety group. We hope that, over time, we will make safety mitigations that make exploitation of Linux kernel vulnerabilities as exhausting as attainable.

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