CVE-2021-28688

Host-wide denial of service via persistent-grant leak

Published Apr 6, 2021 · Updated Aug 3, 2024

Denial of service in Linux's Xen blkback driver allows local users in guest domains to exhaust host resources through persistent grants. The XSA-365 cleanup initialization overwrites pointers that still require cleanup, so the backend fails to release their persistent grants. Reachability requires a malicious or buggy Xen block frontend and persistent grants; the leak can leave zombie domains and exhaust resources across the host.

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 Linux's Xen blkback driver allows local users in guest domains to exhaust host resources through persistent grants. The XSA-365 cleanup initialization overwrites pointers that still require cleanup, so the backend fails to release their persistent grants. Reachability requires a malicious or buggy Xen block frontend and persistent grants; the leak can leave zombie domains and exhaust resources across the host.

The record

CVE
CVE-2021-28688
Published
Apr 6, 2021
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-665, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 6, 2021CVE 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.11 <unspecified
  2. Affected versionversion=5.10.18
  3. Affected versionversion=5.11.1
  4. Affected versionversion=5.12-rc

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3.11 <unspecified; version=5.10.18; version=5.11.1; version=5.12-rc

Published CVSS scores

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

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

CWE-665Improper Initialization
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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