3 ms·
Zapscape (CVE-2026-64561): Guest-to-Host Escape in KVM/x86
- rvz 3mo agoAnother serious critical vulnerability that almost no-one cares about, when they should.
- minimaltom 3mo agoOh yay another one lol. This one seems much more general than the prior one that needed nested page tables. Patch Thursday for cloud VM ppl lol
- metadat 3mo agoDo most cloud providers have live-migration or what is the approach to make this seamless? What kind of interruption might tenants notice?
- cudder 3mo agoIt depends. If you have a plain old VM with no GPU and networked storage it's easy to migrate. If you're using low latency HW on the host it gets a lot trickier. Kuberenetes or some other fleet management helps there, you spin up new nodes and drain the old ones as capacity allows. If you have your PodDisruptionBudgets set right you won't notice much. You can also use ksplice to live patch the vulnerable kernels as a first aid. I'm not an expert but I think there are some limits to what you can accomplish with it. Also guessing that the embargo period allows the big names to roll the patches out gradually enough that you won't see any panic shutdowns.
- minimaltom 3mo agoYeah most cloud providers have live migration and a reasonably-well-tested playbook for updating the node kernel + hypervisor.
- tryauuum 3mo agoDoesn't this one need it as well? I see the shadow mmu
- minimaltom 3mo agoRight, but what x86 KVM setup is there in practice that doesnt present a mmu to its guest and hence keep its own track (shadow) of memory mappings?
- Veserv 3mo agoShadow memory mappings are only needed when you do not have hardware virtualization or when doing nested virtualization. From the page: "it can threaten the guest-host isolation of KVM/x86 hosts that accept untrusted guests and expose nested virtualization" That is not to say that it is not a serious vulnerability though.
- esjeon 2mo agoThis one exploit "shadow MMU" in the nested virtualization path of KVM, so this one is more-limited than EPT/NPT vul'n (KVM defaults to EPT/NPT, nested virt'n is disabled by default). Nested virtualization is rather a niche feature, and, tbh, considering that shadow MMU is highly complicated legacy code (i.e. outside of the main happy path) and has been source of critical vul'n, I would avoid nested virtualization on KVM.
- inigyou 3mo agoEvery LLM bug in the Linux kernel (warehouse rave edit). (This comment is a reference to https://youtu.be/v1Mfirg2-Z8 https://youtu.be/v1Mfirg2-Z8
- eqvinox 2mo agoAnyone know if "-cpu ${CPU},vmx=off,svm=off" in QEMU is a safe workaround for this? (To disable nested virtualization on a per-VM basis. Only against exploitation from within that specific VM, obviously does nothing against users with access to /dev/kvm on the host.) [That did work around Januscape: https://news.ycombinator.com/item?id=48815819 https://news.ycombinator.com/item?id=48815819]
- esjeon 2mo agoThis one(Zapscape) exploits the same module(shadow MMU) as Januscape, so it does workaround the issue. AFAIK the only code paths that activates shadow MMU are (1) lack of hardware EPT/NPT support (2) nested virtualization. Hiding `vmx`/`svm` prevents access to the second code path.
- snvzz 2mo agoIn seL4, a VMM escape, hard as that'd be, yields nothing. VMM handles all VM exceptions, and is just another user program. It has no higher capabilities than the VM itself.
- voidmain 2mo ago> Q: Do you think KVM vulnerabilities will keep appearing? > A: Yes. I recommend establishing a sustainable patching process for host hypervisors. Winter is coming.