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Linux KernelOperating system · Linux

CVE-2021-3759

MEDIUM · 5.5 CVSS v3.1 Published 2022-08-23
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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 memory overflow vulnerability was found in the Linux kernel’s ipc functionality of the memcg subsystem, in the way a user calls the semget function multiple times, creating semaphores. This flaw allows a local user to starve the resources, causing a denial of service. The highest threat from this vulnerability is to system availability.

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

Memory overflow in Linux kernel's memcg subsystem ipc functionality allows local users to repeatedly call semget() to create semaphores and exhaust kernel memory resources, causing denial of service.

MitigationApply kernel patches for CVE-2021-3759; consider system resource limits for semaphore creation via sysctl or cgroup configurations to limit per-user semaphore allocations.

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

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. Confirm the operating system is Linux
    Run 'uname -a' or check /proc/version to verify the kernel is Linux-based
    Affected if The system is not running a Linux kernel (the CVE only affects Linux)
  2. Verify memcg is enabled in the running kernel
    Check if memory cgroups are active by running 'mount | grep cgroup' or checking /sys/fs/cgroup/ for cgroup v1, or /sys/fs/cgroup/unified/ for cgroup v2
    Affected if memcg is enabled and the kernel is Linux - the vulnerability exists in the memcg IPC handling code
  3. Check current semaphore usage
    Run 'ipcs -s' to list current semaphore sets and their memory usage
    Affected if There are many semaphore sets created, indicating potential active exploitation of the memory exhaustion issue
  4. Verify semaphore limits are not configured
    Check /proc/sys/kernel/sem (semaphore parameters) and /proc/sys/fs/sem (if exists) for limits, or run 'sysctl -a | grep sem'
    Affected if No user-level or cgroup-level limits are set on semaphore creation, allowing unlimited semget() calls
  5. Check for resource limit configuration
    Review cgroup memory limits if using cgroups v1/v2, or check /etc/security/limits.conf for user-level semaphore limits
    Affected if No limits are configured in cgroups or PAM limits, meaning any local user can trigger unlimited semaphore creation

A user is affected if running a Linux kernel with memcg enabled and no cgroup or sysctl limits are in place to restrict semaphore creation via semget().

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply kernel patches for CVE-2021-3759; consider system resource limits for semaphore creation via sysctl or cgroup configurations to limit per-user semaphore allocations.

Recommended fix High confidence

Linux kernel >= 5.14.8 or distribution-specific kernel update (Debian: DSA-XXXX-XX, RHEL: kernel-4.18.0-xxx or later)

  1. Update the Linux kernel package to receive the fix for the memcg subsystem resource consumption vulnerability. On Debian 10 (Buster), run: apt-get update && apt-get install linux-image-$(uname -r) or upgrade all packages: apt-get upgrade
  2. After kernel update, reboot the system to load the fixed kernel: systemctl reboot
  3. Verify the running kernel version after reboot: uname -r
  4. For RHEL/RHEL-based distributions, apply the latest kernel security updates: yum update kernel
Caveat Kernel upgrades 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
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,480
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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-2021-3759 in production — separate from our analysis above.

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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
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