CVE-2021-28038

Host-wide denial of service via ignored mapping errors

Published Mar 5, 2021 · Updated Aug 3, 2024

Denial of service in Linux kernel xen-netback through 5.11.3 allows guest OS users to disrupt the host via a misbehaving PV frontend. The netback path effectively ignores grant-mapping failures at a relevant function call, so a memory-allocation failure can crash the backend. Only Linux backends running in Xen PV mode are affected; HVM and PVH modes are not, while a backend crash typically interrupts the entire host.

CVSS severity6.5
Medium
EPSS probability0.71%
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 kernel xen-netback through 5.11.3 allows guest OS users to disrupt the host via a misbehaving PV frontend. The netback path effectively ignores grant-mapping failures at a relevant function call, so a memory-allocation failure can crash the backend. Only Linux backends running in Xen PV mode are affected; HVM and PVH modes are not, while a backend crash typically interrupts the entire host.

The record

CVE
CVE-2021-28038
Published
Mar 5, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-770, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 5, 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?

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

6.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
4.9NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:C

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation

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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