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Zapscape: Guest-to-Host Escape in KVM/x86 (CVE-2026-64561)

tentortentor Member, Host Rep

This is a report on "Zapscape (CVE-2026-64561)", a KVM escape vulnerability that lets a guest escape to the host in KVM/x86, that is, on both Intel and AMD hosts.

Zapscape is a use-after-free vulnerability in the shadow MMU emulation of KVM/x86, specifically in the recursive "zap" path that runs when shadow
pages are reclaimed. It can trigger the bug with guest-side actions alone to corrupt the host kernel's shadow page, and it can threaten the guest-host isolation of KVM/x86 hosts that accept untrusted guests and
expose nested virtualization, particularly multi-tenant x86 public clouds.

However, unlike the previously published Januscape (CVE-2026-53359), on Intel it can be triggered only when both EPT page walk length 4 and 5 are
exposed to L1. On AMD there is no such constraint.

This vulnerability was reported to [email protected] and is now patched in mainline. It covers the range from f95eec9bed76 (2020-07-08) to
2abd5287f083 (2026-07-21): https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2abd5287f083

For detailed information about the vulnerability and follow-up updates, please see: https://zapscape.io

Comments

  • To quote the famous bowl of petunias, "Oh no, not again...".

  • DecicusDecicus Member
    edited 4:20PM

    Is it too late to become a farmer?

    I don't need to kernel patch a cow, for example.

    Thanked by 3layer7 OhJohn barbaros
  • rpqurpqu Member

    fuck

  • stable_geniusstable_genius Member
    edited 4:39PM

    With so many KVM vulnerabilities I guess it will be safer to run everything in qemu CPU emulation mode, no KVM.

    Jokes aside, I found one decent use for that.

  • deafcondeafcon Member

    @Decicus said:
    Is it too late to become a farmer?

    I don't need to kernel patch a cow, for example.

    There's got to be a joke about a cow in a corn field in there somewhere, but I can't find it.

  • The sun is going down!

  • tentortentor Member, Host Rep
    edited 4:41PM

    People miss the most important remark

    it can threaten the guest-host isolation of KVM/x86 hosts that accept untrusted guests and expose nested virtualization

    Thanked by 1Nadwey
  • OhJohnOhJohn Member

    Hey wait, it's not Friday yet.

    Thanked by 1tentor
  • And there is also this beauty, CVE-2026-64564, an LPE via SCTP, including container-to-host escape

    Thanked by 1tentor
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