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Linux KernelOperating system · Linux

CVE-2021-28715

MEDIUM · 6.5 CVSS v3.1 Published 2022-01-06
Fix available
A fix is available. Upgrade to 5.15.0 or later.
See remediation →
67/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Guest can force Linux netback driver to hog large amounts of kernel memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Incoming data packets for a guest in the Linux kernel's netback driver are buffered until the guest is ready to process them. There are some measures taken for avoiding to pile up too much data, but those can be bypassed by the guest: There is a timeout how long the client side of an interface can stop consuming new packets before it is assumed to have stalled, but this timeout is rather long (60 seconds by default). Using a UDP connection on a fast interface can easily accumulate gigabytes of data in that time. (CVE-2021-28715) The timeout could even never trigger if the guest manages to have only one free slot in its RX queue ring page and the next package would require more than one free slot, which may be the case when using GSO, XDP, or software hashing. (CVE-2021-28714)

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a vulnerability in the Linux kernel's Xen netback driver (network backend). A malicious guest VM can bypass existing rate-limiting controls by not consuming packets from its RX queue, allowing gigabytes of data to accumulate in host kernel memory over the 60-second timeout period, leading to memory exhaustion on the host.

MitigationApply the upstream Linux kernel patch to Xen host systems. As a workaround, consider implementing network quotas or monitoring guest RX queue utilization to detect abnormal memory accumulation patterns.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:< 5.15.0
Debian LinuxOperating system
Affected:= 9.0= 10.0= 11.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm system is running as a Xen host
    Run 'xl info' or 'xl list' to list Xen virtual machines. If these commands fail, the system may not be a Xen host.
    Affected if The system is not a Xen host (not running Xen hypervisor)
  2. Verify Xen netback driver is loaded
    Run 'lsmod | grep xen_netback' to check if the netback driver module is loaded.
    Affected if The xen_netback module is not loaded (the driver is not in use)
  3. Check installed kernel version
    Run 'uname -r' to get the running kernel version.
    Affected if Kernel version is 5.15.0 or higher (漏洞仅影响低于5.15.0的内核)
  4. Check Debian release version
    If running Debian, run 'cat /etc/debian_version' to identify the release.
    Affected if Running Debian 9.0, 10.0, or 11.0 and the kernel is from the affected range

A system is affected if it is a Xen host running kernel version below 5.15.0 with the xen_netback driver loaded, particularly on Debian 9.0-11.0.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.15.0 or later
Fixed in 5.15.0
Interim mitigation

Apply the upstream Linux kernel patch to Xen host systems. As a workaround, consider implementing network quotas or monitoring guest RX queue utilization to detect abnormal memory accumulation patterns.

Recommended fix High confidence

Linux Kernel 5.15.0 or later; Debian stable kernels with backported security fixes

  1. Upgrade Linux kernel to version 5.15.0 or later to obtain the fix for CVE-2021-28715
  2. For Debian systems, apply kernel updates from Debian security repositories: 'apt-get update && apt-get upgrade' or 'apt-get dist-upgrade'
  3. After kernel upgrade, reboot the system to load the patched kernel
  4. Verify the running kernel version with 'uname -r' to confirm the upgrade was successful
  5. For production systems, test the kernel upgrade in a staging environment before deploying broadly
Caveat Kernel upgrades may require system reboot and could have compatibility implications with custom kernel modules or specific hardware drivers; ensure backup and staging test before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-28715 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data