CVE-2021-28691

Name: CVE-2021-28691
Creator: NVD / NIST
Published: 2021-06-29T12:15:08.543+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.8/10EPSS 0.36%

Last modified Jun 17, 2026

CVE-2021-28691 is a high-severity vulnerability rated 7.8/10 on the CVSS scale. Guest triggered use-after-free in Linux xen-netback A malicious or buggy network PV frontend can force Linux netback to disable the interface and terminate the receive kernel thread associated with queue 0 in response to the frontend sending a malformed packet. Such kernel thread termination will lead to a use-after-free in Linux netback when the backend is destroyed, as the kernel thread associated with queue 0 will have already exited and thus the call to kthread_stop will be performed against a stale pointer.. EPSS estimates a 0.36% chance of exploitation in the next 30 days.

Description

Guest triggered use-after-free in Linux xen-netback A malicious or buggy network PV frontend can force Linux netback to disable the interface and terminate the receive kernel thread associated with queue 0 in response to the frontend sending a malformed packet. Such kernel thread termination will lead to a use-after-free in Linux netback when the backend is destroyed, as the kernel thread associated with queue 0 will have already exited and thus the call to kthread_stop will be performed against a stale pointer.

Metrics

CVSS 3.1

7.8/10

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

EPSS Probability

0.36%

28.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-416

Affected Software

Vendor	Product	Versions
Linux	Linux Kernel	>= 5.5.0, < 5.12.2
Netapp	Cloud Backup	All versions
Netapp	H410c Firmware	All versions
Netapp	H300s Firmware	All versions
Netapp	H500s Firmware	All versions
Netapp	H700s Firmware	All versions
Netapp	H300e Firmware	All versions
Netapp	H500e Firmware	All versions
Netapp	H700e Firmware	All versions
Netapp	H410s Firmware	All versions

References

https://security.gentoo.org/glsa/202107-30Third Party Advisory
https://security.netapp.com/advisory/ntap-20210805-0002/Third Party Advisory
https://xenbits.xenproject.org/xsa/advisory-374.txtThird Party Advisory
https://security.gentoo.org/glsa/202107-30Third Party Advisory
https://security.netapp.com/advisory/ntap-20210805-0002/Third Party Advisory
https://xenbits.xenproject.org/xsa/advisory-374.txtThird Party Advisory

Timeline

Published: Jun 29, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-28691?

How severe is CVE-2021-28691?

CVE-2021-28691 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 0.36% probability of exploitation in the next 30 days.

How do I fix CVE-2021-28691?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-28691?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST