Host MSR access bypass via VMCB12 double fetch
Published Jul 22, 2021 · Updated Aug 3, 2024
Use-after-free in Linux kernel KVM before 5.11.12 allows guest OS users on AMD hosts to bypass host MSR access controls. nested_svm_vmrun double-fetches the guest-controlled VMCB12, allowing a concurrent nested VMRUN to free an MSR permission bitmap still in use and corrupt the saved host state. Exploitation requires AMD KVM with nested guests and winning the TOCTOU race; successful exploitation grants unrestricted access to host MSRs.
Summary
What happened
Use-after-free in Linux kernel KVM before 5.11.12 allows guest OS users on AMD hosts to bypass host MSR access controls. nested_svm_vmrun double-fetches the guest-controlled VMCB12, allowing a concurrent nested VMRUN to free an MSR permission bitmap still in use and corrupt the saved host state. Exploitation requires AMD KVM with nested guests and winning the TOCTOU race; successful exploitation grants unrestricted access to host MSRs.
The record
- CVE
- CVE-2021-29657
- Published
- Jul 22, 2021
- Updated
- Aug 3, 2024
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-367, CWE-416, T1068
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 22, 2021CVE publishedPublication date reported by the CVE source.
- Aug 3, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What conditions does exploitation require?
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
- Project Zero nested_svm_vmrun double-fetch proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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