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CVE Record

CVE-2021-47060: KVM: Stop looking for coalesced MMIO zones if the bus is destroyed

In the Linux kernel, the following vulnerability has been resolved: KVM: Stop looking for coalesced MMIO zones if the bus is destroyed Abort the walk of coalesced MMIO zones if kvm_io_bus_unregister_dev() fails to allocate memory for the new instance of the bus. If it can't instantiate a new bus, unregister_dev() destroys all devices _except_ the target device. But, it doesn't tell the caller that it obliterated the bus and invoked the destructor for all devices that were on the bus. In the coalesced MMIO case, this can result in a deleted list entry dereference due to attempting to continue iterating on coalesced_zones after future entries (in the walk) have been deleted. Opportunistically add curly braces to the for-loop, which encompasses many lines but sneaks by without braces due to the guts being a single if statement.

MediumCVSS 6Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-47060 is a Linux kernel KVM flaw in coalesced MMIO cleanup handling. Under a specific local, highly privileged condition, KVM can continue using list entries after related devices were destroyed, risking host confidentiality and availability impacts. This is most relevant to Linux virtualization hosts, not ordinary remote network exposure.

Executive priority

Treat as a moderate-priority infrastructure hygiene issue. Patch KVM-capable Linux hosts through normal kernel maintenance, with faster handling for shared virtualization or cloud hosts where privileged local access boundaries matter.

Technical view

The bug is in KVM’s coalesced MMIO zone walk after kvm_io_bus_unregister_dev() fails to allocate a replacement bus. The unregister path can destroy other bus devices without clearly signaling that state, so iteration may continue over deleted coalesced_zones entries, causing deleted list entry dereference. CVSS is 6.0 with local attack vector and high privileges required.

Likely exposure

Exposure is likely limited to Linux systems using KVM on affected kernel builds or downstream packages carrying the vulnerable code. The provided source data names Linux kernel versions and stable commit references, but package-level distro status must be verified with the relevant vendor.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation evidence. The CVSS vector requires local access and high privileges, which reduces broad internet-scale risk but keeps the issue important for shared virtualization, cloud, lab, and hosting environments.

Researcher notes

Evidence supports a kernel logic/use-after-delete style issue during KVM bus unregister failure handling. The prompt does not include proof-of-concept details, exploit reports, or distro fix matrices. Avoid assuming remote exploitability or active attacks without additional sourced evidence.

Mitigation direction

  • Inventory Linux hosts running KVM or virtualization workloads.
  • Apply vendor kernel updates containing the referenced stable fixes.
  • Check distro advisories for package-specific fixed versions.
  • Restrict privileged KVM and VM management access.
  • Prioritize hypervisor hosts over non-virtualization Linux systems.

Validation and detection

  • Confirm kernel versions on KVM-capable hosts.
  • Map installed packages to vendor advisories for CVE-2021-47060.
  • Check whether referenced stable commits are present in source builds.
  • Review virtualization hosts for untrusted privileged users or tenants.
  • Document any unsupported kernels requiring upgrade planning.
Prepared
Confidence
high
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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CVE-2021-47060 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:H

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.

1CVSS vectors
3Timeline events
2ADP providers
6Source links

SSVC decision data

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

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:H0.85.2CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

6Medium
CVSS 3.1 vector shape for CVE-2021-47060Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

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
cvssV3_1other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux41b2ea7a6a11e2b1a7f2c29e1675a709a6b2b98d, f65886606c2d3b562716de030706dfe1bea4ed5e, f65886606c2d3b562716de030706dfe1bea4ed5e, f65886606c2d3b562716de030706dfe1bea4ed5e, f65886606c2d3b562716de030706dfe1bea4ed5e, f0dfffce3f4ffd5f822568a4a6fb34c010e939d1, 840e124f89a5127e7eb97ebf377f4b8ca745c070, 40a023f681befd9b2862a3c16fb306a38b359ae5, 19184bd06f488af62924ff1747614a8cb284ad63, 68c125324b5e1d1d22805653735442923d896a1dunaffected
LinuxLinux5.9, 0, 5.4.119, 5.10.37, 5.11.21, 5.12.4, 5.13affected
Weakness

CWE details

No CWE listed

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