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Linux KernelOperating system · Linux

CVE-2021-3669

MEDIUM · 5.5 CVSS v3.1 Published 2022-08-26
Fix available
A fix is available. Upgrade to 2.7 or later.
See remediation →
57/100
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
A flaw was found in the Linux kernel. Measuring usage of the shared memory does not scale with large shared memory segment counts which could lead to resource exhaustion and DoS.

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

A flaw in the Linux kernel's shared memory (shm) subsystem causes measurement of shared memory usage to not scale properly with large numbers of shared memory segments. The algorithm used to calculate/measure shm usage becomes inefficient at scale, leading to excessive resource consumption (CPU/memory) and potential denial of service.

MitigationApply the upstream Linux kernel patch for CVE-2021-3669 which improves the scalability of shared memory usage measurement. As a compensating control, consider limits on the number and size of shared memory segments via sysctl parameters (kernel.shmmax, kernel.shmall).

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:all versions
Debian LinuxOperating system
Affected:= 10.0= 11.0
FedoraOperating system
Affected:= 34
Build Of QuarkusApplication
Affected:>= 2.0, < 2.7
Developer ToolsApplication
Affected:= 1.0
Enterprise LinuxOperating system
Affected:= 6.0= 7.0= 8.0
Enterprise Linux AusOperating system
Affected:= 8.6
Enterprise Linux For Ibm Z SystemsOperating system
Affected:= 8.0

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
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/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. Check the kernel version
    Run 'uname -r' to get the running kernel version. Compare it against any available patched versions in your distribution's security advisories.
    Affected if The kernel version is unpatched and the system has multiple shared memory segments in use.
  2. Identify shared memory segments in use
    Run 'ipcs -m' to list all shared memory segments currently attached on the system. Count the number of segments displayed.
    Affected if There are hundreds or thousands of shared memory segments active, triggering the inefficient measurement algorithm.
  3. Check system shm limits
    Run 'sysctl kernel.shmmax kernel.shmall' or view '/proc/sys/kernel/shmmax' and '/proc/sys/kernel/shmall' to see configured shared memory limits.
    Affected if High or unlimited shm limits are set, allowing creation of many segments that could be measured inefficiently.
  4. Monitor CPU usage during shm operations
    Observe system CPU usage when operations involving shared memory occur, such as running 'ipcs -m' or attaching/detaching segments.
    Affected if CPU usage spikes or system becomes unresponsive during shared memory measurement operations.

A system is affected if it runs an unpatched kernel and has a large number of shared memory segments in active use, causing measurable performance degradation during shm-related operations.

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 2.7 or later
Fixed in 2.7
Interim mitigation

Apply the upstream Linux kernel patch for CVE-2021-3669 which improves the scalability of shared memory usage measurement. As a compensating control, consider limits on the number and size of shared memory segments via sysctl parameters (kernel.shmmax, kernel.shmall).

Recommended fix Moderate confidence

Kernel version containing the fix for CVE-2021-3669 (consult vendor advisories for exact version)

  1. 1. Identify your current kernel version using 'uname -r'
  2. 2. Check your distribution's security advisories for CVE-2021-3669 to obtain the fixed kernel version
  3. 3. For RHEL/CentOS/Enterprise Linux: Run 'yum update kernel' or 'dnf update kernel'
  4. 4. For Debian/Ubuntu: Run 'apt update && apt install linux-image-generic'
  5. 5. For Fedora: Run 'dnf update kernel'
  6. 6. Reboot the system to load the new kernel: 'systemctl reboot'
  7. 7. Verify the new kernel is running: 'uname -r'
  8. 8. Confirm the vulnerability is mitigated by checking that shared memory measurement scales properly
Caveat Kernel updates may require system reboot and could have compatibility implications with custom kernel modules or specific hardware 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
  • Testing12.0 h
  • Review / QA6.0 h
30.0 hours of engineering $5,120
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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-2021-3669 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