CVE-2021-28691

Dom0 crash via stale receive-thread pointer

Published Jun 29, 2021 · Updated Aug 3, 2024

Use-after-free in Linux xen-netback 5.5 and later allows guest OS users to crash dom0 through a malformed PV network packet. The packet makes xen-netback stop queue 0's receive thread, but backend teardown later passes the freed thread pointer to kthread_stop. The guest must use a PV network frontend; x86 guests restricted to emulated network cards do not reach the flaw.

CVSS severity7.8
High
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Linux xen-netback 5.5 and later allows guest OS users to crash dom0 through a malformed PV network packet. The packet makes xen-netback stop queue 0's receive thread, but backend teardown later passes the freed thread pointer to kthread_stop. The guest must use a PV network frontend; x86 guests restricted to emulated network cards do not reach the flaw.

The record

CVE
CVE-2021-28691
Published
Jun 29, 2021
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 29, 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=5.5.0 <unspecified

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.5.0 <unspecified

Published CVSS scores

7.8NISTCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.6NISTAV:L/AC:L/Au:N/C:P/I:P/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.

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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-416Use After Free
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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