Service interruption via reused shadow-page permissions
Published Aug 8, 2021 · Updated Aug 4, 2024
Improper access control in Linux kernel KVM before 5.12.11 allows guest OS users to interrupt service through crafted guest memory access. In arch/x86/kvm/mmu/paging_tmpl.h, KVM reuses the last non-leaf entry's effective permissions instead of intersecting permissions inherited from every parent, allowing a shadow page created under one access path to be reused under a less permissive path. Exploitation requires a virtual machine with TDP disabled and shared guest page tables whose ancestors grant different permissions; the incorrect reuse suppresses an expected guest protection fault and VM exit.
Summary
What happened
Improper access control in Linux kernel KVM before 5.12.11 allows guest OS users to interrupt service through crafted guest memory access. In arch/x86/kvm/mmu/paging_tmpl.h, KVM reuses the last non-leaf entry's effective permissions instead of intersecting permissions inherited from every parent, allowing a shadow page created under one access path to be reused under a less permissive path. Exploitation requires a virtual machine with TDP disabled and shared guest page tables whose ancestors grant different permissions; the incorrect reuse suppresses an expected guest protection fault and VM exit.
The record
- CVE
- CVE-2021-38198
- Published
- Aug 8, 2021
- Updated
- Aug 4, 2024
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- T1499.004
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 8, 2021CVE publishedPublication date reported by the CVE source.
- Aug 4, 2024Record updatedLatest update available in the CVE record.
Exploitability
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What is affected?
Affected products and versions are unavailable in this record.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- KVM shadow-page permission test codeproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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