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Fencer Vulns
high 7.8

CVE-2021-28691 json

Guest triggered use-after-free in Linux xen-netback A malicious or buggy network PV frontend can force Linux netback to disable the interfa…

published 2021-06-29 5 y ago modified 2026-08-26 2 mo ago also EUVD-2021-15348

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 30%
public exploits
0
none known

Summary

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.

Patch / fix

  • linux linux_kernel 5.10.43
  • linux Debian 14, Debian 13, Debian 12 5.10.46-1

debian advisories DEBIAN-CVE-2021-28691

  • linux-aws-5.8 Ubuntu 20.04 LTS 5.8.0-1042.44~20.04.1
  • linux-gcp-5.8 Ubuntu 20.04 LTS 5.8.0-1039.41
  • linux-aws-5.11 Ubuntu 20.04 LTS 5.11.0-1016.17~20.04.1
  • linux-gcp-5.11 Ubuntu 20.04 LTS 5.11.0-1017.19~20.04.1
  • linux-hwe-5.11 Ubuntu 20.04 LTS 5.11.0-34.36~20.04.1
  • linux-oem-5.10 Ubuntu 20.04 LTS 5.10.0-1038.40
  • linux-azure-5.8 Ubuntu 20.04 LTS 5.8.0-1040.43~20.04.1
  • linux-azure-5.11 Ubuntu 20.04 LTS 5.11.0-1013.14~20.04.1

ubuntu advisories UBUNTU-CVE-2021-28691

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel CBL-Mariner 2.0 5.10.78.1-1

azure linux advisories AZL-6537

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-28691 updated cvss 6.2

xen: guest triggered use-after-free in Linux xen-netback (XSA-374)

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.36% chance of exploitation in the next 30 days, higher than 30% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 4.6 AV:L/AC:L/Au:N/C:P/I:P/A:P

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.