CVE-2021-28711

Guest service interruption via blkfront event storms

Published Jan 5, 2022 · Updated Aug 3, 2024

Denial of service in Xen blkfront in Linux allows guest OS users controlling a PV backend to interrupt serviced guest workloads. The blkfront driver processes backend notifications without late-EOI event-channel deferral, allowing repeated events to monopolize guest interrupt handling. Exploitation requires control of a PV backend in a Xen driver domain; the host remains unaffected while serviced guests lose availability.

CVSS severity6.5
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Xen blkfront in Linux allows guest OS users controlling a PV backend to interrupt serviced guest workloads. The blkfront driver processes backend notifications without late-EOI event-channel deferral, allowing repeated events to monopolize guest interrupt handling. Exploitation requires control of a PV backend in a Xen driver domain; the host remains unaffected while serviced guests lose availability.

The record

CVE
CVE-2021-28711
Published
Jan 5, 2022
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 5, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

2.1NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
6.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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