medium CVSS 5.5 EPSS <0.1%

CVE-2021-47450·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Fix host stage-2 PGD refcount The KVM page-table library refcounts the pages of concatenated stage-2 PGDs individually. However, when running KVM in protected mode, the host's stage-2 PGD is currently managed by EL2 as a single high-order compound page, which can cause the refcount of the tail pages to reach 0 when they shouldn't, hence corrupting the page-table. Fix this by introducing a new hyp_split_page() helper in the EL2 page allocator (matching the kernel's split_page() function), and make use of it from host_s2_zalloc_pages_exact().

Severity
medium
Software
Kernel
Fixed in
5.14.15
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 3% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

From: 5.13

Until: 5.14.15

Fixed in: 5.14.15

How to fix this CVE

Update your Linux kernel to version 5.14.15 or later to resolve a page table refcount corruption issue in ARM64 KVM protected mode environments. This vulnerability affects the management of concatenated stage-2 page global directories and can lead to system instability. Apply the kernel update immediately if you are running KVM on ARM64 systems with kernel versions 5.13 through 5.14.14.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check the installed kernel version with 'uname -r' and compare against the affected range (5.13 to 5.14.14)
  2. Step 2: Verify if KVM is enabled on the system by running 'grep -i kvm /proc/cpuinfo' and 'lsmod | grep kvm'
  3. Step 3: On ARM64 systems, check for KVM protected mode usage with 'cat /sys/module/kvm_arm/parameters/protected_mode' or 'cat /sys/firmware/efi/fw_platform_size'
  4. Step 4: After patching, confirm the new kernel version with 'uname -r' shows version 5.14.15 or later

FAQ

What is CVE-2021-47450?

This vulnerability affects the Linux kernel's KVM implementation on ARM64 systems, where improper page table reference counting for concatenated stage-2 page global directories can lead to memory corruption when KVM runs in protected mode.

Is CVE-2021-47450 being actively exploited?

No, this vulnerability is not currently being actively exploited in the wild and has not been added to the CISA Known Exploited Vulnerabilities catalog.

What versions of Kernel are affected by CVE-2021-47450?

Linux kernel versions 5.13 through 5.14.14 are affected. Kernel 5.14.15 and later versions contain the fix.

How do I check if my server is vulnerable to CVE-2021-47450?

Run 'uname -r' to check your kernel version. If it shows 5.13.x through 5.14.14 and the system is ARM64-based with KVM enabled, your system is vulnerable.

Does Defensia detect CVE-2021-47450?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2021-47450 will appear in your dashboard with remediation steps.

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References

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