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CVE Record

CVE-2021-47217: x86/hyperv: Fix NULL deref in set_hv_tscchange_cb() if Hyper-V setup fails

In the Linux kernel, the following vulnerability has been resolved: x86/hyperv: Fix NULL deref in set_hv_tscchange_cb() if Hyper-V setup fails Check for a valid hv_vp_index array prior to derefencing hv_vp_index when setting Hyper-V's TSC change callback. If Hyper-V setup failed in hyperv_init(), the kernel will still report that it's running under Hyper-V, but will have silently disabled nearly all functionality. BUG: kernel NULL pointer dereference, address: 0000000000000010 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.15.0-rc2+ #75 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:set_hv_tscchange_cb+0x15/0xa0 Code: <8b> 04 82 8b 15 12 17 85 01 48 c1 e0 20 48 0d ee 00 01 00 f6 c6 08 ... Call Trace: kvm_arch_init+0x17c/0x280 kvm_init+0x31/0x330 vmx_init+0xba/0x13a do_one_initcall+0x41/0x1c0 kernel_init_freeable+0x1f2/0x23b kernel_init+0x16/0x120 ret_from_fork+0x22/0x30

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel reliability flaw in Hyper-V-related code. If Hyper-V setup fails but the kernel still believes it is running under Hyper-V, later virtualization initialization can dereference a null pointer and crash the kernel.

Executive priority

Treat as a targeted availability risk for Linux virtualization environments. Prioritize normal kernel patching for affected Hyper-V-adjacent systems, but there is no source-backed evidence of active exploitation or critical business-wide urgency.

Technical view

set_hv_tscchange_cb() could read hv_vp_index without confirming the array was valid. After a failed hyperv_init(), most Hyper-V functionality is disabled, but Hyper-V presence may still be reported. The cited crash occurs during KVM/VMX initialization with a kernel NULL pointer dereference.

Likely exposure

Exposure appears limited to affected Linux kernels in Hyper-V or Hyper-V-presenting environments, especially systems using KVM/VMX initialization after partial Hyper-V setup failure. The source bundle does not identify specific distributions or cloud platforms.

Exploitation context

The bundle does not show active exploitation, KEV listing, public exploit use, or remote attack requirements. Evidence supports a kernel crash condition from a failed setup state, not weaponized exploitation.

Researcher notes

The root issue is missing validation of hv_vp_index before dereference after Hyper-V initialization failure. The affected range and fixed branch details should be confirmed through downstream vendor advisories because the CVE bundle lists upstream stable references, not distro package mappings.

Mitigation direction

  • Update to a Linux kernel containing the cited stable fixes or a vendor backport.
  • Check Linux distribution advisories for CVE-2021-47217 package status.
  • Prioritize Hyper-V guest and virtualization-enabled Linux images.
  • Avoid assuming unaffected status from version strings alone; verify vendor backports.

Validation and detection

  • Inventory Linux kernel versions across Hyper-V and virtualization-enabled systems.
  • Confirm whether vendor kernels include the relevant stable fix commits.
  • Review kernel logs for NULL dereference traces involving set_hv_tscchange_cb.
  • Test updated images in Hyper-V-like environments before rollout.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux93286261de1b46339aa27cd4c639b21778f6cade, 93286261de1b46339aa27cd4c639b21778f6cade, 93286261de1b46339aa27cd4c639b21778f6cade, 93286261de1b46339aa27cd4c639b21778f6cade, 93286261de1b46339aa27cd4c639b21778f6cadeunaffected
LinuxLinux4.16, 0, 4.19.218, 5.4.162, 5.10.82, 5.15.5, 5.16affected
Weakness

CWE details

No CWE listed

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