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VulnerabilityPublished Updated

CVE-2026-99082: Linux kernel · KVM: x86: Use active memslots for the per-vCPU MMIO cache

Source GCVE Database

0
Authoritative record:CVE-2026-99082· High 8.8

Not known to be exploited · CVSS 8.8 High · fixed in e792a9ace39d2812a5b342a1987186c7bc653204 : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score
8.8High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 4% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in e792a9ace39d2812a5b342a1987186c7bc653204, b3e6212dea2e4328a841ceb37f377583176dc735, a63f79d9da9468952396af73e1e53330845cf876 +2
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 23 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 699023e239658e62da6f42f47d31b54788521ec1, < e792a9ace39d2812a5b342a1987186c7bc653204
Fixed in
  • e792a9ace39d2812a5b342a1987186c7bc653204
LinuxLinuxAffected
  • ≥ 699023e239658e62da6f42f47d31b54788521ec1, < b3e6212dea2e4328a841ceb37f377583176dc735
Fixed in
  • b3e6212dea2e4328a841ceb37f377583176dc735
LinuxLinuxAffected
  • ≥ 699023e239658e62da6f42f47d31b54788521ec1, < a63f79d9da9468952396af73e1e53330845cf876
Fixed in
  • a63f79d9da9468952396af73e1e53330845cf876
LinuxLinuxAffected
  • ≥ 699023e239658e62da6f42f47d31b54788521ec1, < 2566780c684c9c21241d409d790087c73070f312
Fixed in
  • 2566780c684c9c21241d409d790087c73070f312
LinuxLinuxAffected
  • ≥ 699023e239658e62da6f42f47d31b54788521ec1, < 7fd4e64f4bbc8c35ae8f0d2a1fb5b77a76d5b4fd
Fixed in
  • 7fd4e64f4bbc8c35ae8f0d2a1fb5b77a76d5b4fd
LinuxLinuxAffected
  • =4.2
Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Use active memslots for the per-vCPU MMIO cache KVM tags the per-vCPU MMIO cache with a memslot generation so that a memslot update invalidates cached MMIO information. Both the fill and validation paths use kvm_memslots(), which unconditionally selects address space 0, even when the vCPU is running in SMM and using address space 1. Commit 56f17dd3fbc4 ("kvm: x86: fix stale mmio cache bug") added the memslot generation to the cache key so that a memslot update could not leave a stale entry valid. When commit 699023e23965 ("KVM: x86: add SMM to the MMU role, support SMRAM address space") added the SMM address space, these helpers were not converted to use the active memslots. Consequently, an update to the SMM memslots can leave an entry from the old SMM address space apparently valid after the vCPU returns to the normal address space. A guest can then cause an access to valid RAM at the same GFN to be returned to userspace as KVM_EXIT_MMIO. Completing that exit through the VMM's RAM address space writes the backing page without going through KVM's write-tracking path. If the page backs a nested EPT table, KVM can continue using shadow translations derived from the old contents. The WARN_ON_ONCE() in kvm_mmu_write_protect_fault() catches this invalid cache and memslot combination. Use the vCPU's active memslots when caching and validating the entry. Memslot generations are unique across address spaces, so the generation also distinguishes the normal and SMM views. This matches the MMIO SPTE cache, which already uses kvm_vcpu_memslots(). On an unpatched current-mainline kernel, a regression test that fills the cache in SMM and updates only the SMM memslots fails the intended RAM write and triggers the kvm_mmu_write_protect_fault() warning. With this change, the same test completes the RAM write without a warning. The x86/smm_test, set_memory_region_test, and memslot_modification_stress_test selftests also pass.

References

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