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Linux KernelOperating system · Linux

CVE-2021-28714

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 · moderate confidence

The Linux netback driver in Xen hypervisors fails to properly limit kernel memory buffering for guest VMs. A malicious guest can exploit the RX queue slot mechanism by ensuring only one slot is free while incoming packets require multiple slots (as with GSO, XDP, or software hashing), preventing the 60-second stall timeout from ever triggering and causing unbounded memory accumulation on the host.

MitigationApply kernel patches for CVE-2021-28714 to fix the netback driver's queue management logic. Consider reducing the default timeout as a temporary measure until patches are applied.

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:= 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. Verify Xen hypervisor environment
    Check if the system is running as a Xen hypervisor host by examining /proc/xen or running 'xl list' or 'xm list' if xen-utils are installed
    Affected if The system is not a Xen hypervisor host (netback runs only on Xen dom0)
  2. Check kernel version
    Run 'uname -r' or 'cat /proc/version' to obtain the running kernel version
    Affected if Kernel version is 5.15.0 or higher (the fix was merged in 5.15.0)
  3. Confirm netback driver is active
    Run 'lsmod | grep xen_netback' or check 'modinfo xen_netback' to see if the Xen network backend driver is loaded
    Affected if The xen_netback module is not loaded (the vulnerability only affects systems using this driver)
  4. Identify dom0 network interfaces
    Check if network interfaces are using the netback backend by examining 'ethtool -i <interface>' output for xen_netback, or check 'brctl show' for xen bridges
    Affected if No network interfaces are bound to xen_netback (vulnerability requires active netback-managed interfaces)

A user is affected if this system is a Xen hypervisor dom0 running kernel versions below 5.15.0 with the xen_netback driver active and managing network interfaces.

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 kernel patches for CVE-2021-28714 to fix the netback driver's queue management logic. Consider reducing the default timeout as a temporary measure until patches are applied.

Recommended fix High confidence

Linux Kernel 5.15.0 or later; Debian kernels with the security fix applied

  1. Upgrade Linux kernel to version 5.15.0 or later to receive the fix for the netback driver resource allocation vulnerability
  2. For Debian 10 (Buster): Apply Debian kernel security updates or upgrade to a kernel version that includes the fix
  3. For Debian 11 (Bullseye): Apply Debian kernel security updates or upgrade to a kernel version that includes the fix
Caveat Kernel upgrades may require system reboot; ensure compatibility with existing system configuration and drivers

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 / QA3.0 h
21.0 hours of engineering $3,680
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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-2021-28714 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