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Linux KernelOperating system · Linux

CVE-2021-4157

HIGH · 8.0 CVSS v3.1 Published 2022-03-25
Fix available
A fix is available. Upgrade to 4.4.269 / 4.9.269 or later.
See remediation →
82/100
Remediation priority · High
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
An out of memory bounds write flaw (1 or 2 bytes of memory) in the Linux kernel NFS subsystem was found in the way users use mirroring (replication of files with NFS). A user, having access to the NFS mount, could potentially use this flaw to crash the system or escalate privileges on the system.

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

An out-of-bounds write vulnerability (1-2 bytes) in the Linux kernel NFS subsystem related to file mirroring/replication operations. A user with access to an NFS mount can write beyond intended memory bounds, potentially crashing the system or achieving privilege escalation.

MitigationApply the relevant Linux kernel security patches for this NFS subsystem vulnerability. Restrict NFS mount access to trusted users and systems to reduce the attack surface until patching can be completed.

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:>= 4.0, < 4.4.269>= 4.5, < 4.9.269>= 4.10, < 4.14.233>= 4.15, < 4.19.191>= 4.20, < 5.4.120>= 5.5, < 5.10.38>= 5.11, < 5.11.22>= 5.12, < 5.12.5
FedoraOperating system
Affected:= 35
H300e FirmwareOperating system
Affected:all versions
H300s FirmwareOperating system
Affected:all versions
H500e FirmwareOperating system
Affected:all versions
H500s FirmwareOperating system
Affected:all versions
H700e FirmwareOperating system
Affected:all versions
H700s FirmwareOperating system
Affected:all versions

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
Adjacent
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 running Linux kernel version
    Run `uname -r` or check `/proc/version` to obtain the kernel version. Compare it against the affected ranges: < 4.4.269, >= 4.5 and < 4.9.269, >= 4.10 and < 4.14.233, >= 4.15 and < 4.19.191, >= 4.20 and < 5.4.120, >= 5.5 and < 5.10.38, >= 5.11 and < 5.11.22, >= 5.12 and < 5.12.5
    Affected if The kernel version falls within any of these ranges and the system uses NFS functionality
  2. Determine if NFS is mounted or in use
    Run `mount | grep nfs` or `showmount -e` to check for active NFS mounts or exports. Also check `nfsstat -c` or review /proc/fs/nfsfs/ for NFS client/server activity
    Affected if NFS shares are mounted or the system is acting as an NFS server or client
  3. Identify the operating system distribution and version
    Check the OS by running `cat /etc/os-release` or `hostnamectl`. For Fedora systems, verify if the version is 35
    Affected if The system is Fedora 35 regardless of kernel version, or if running an affected kernel on any Fedora release
  4. Check if this is a NetApp H-series storage system
    If the target is a NetApp H300e, H300s, H500e, H500s, H700e, or H700s device, check the firmware version via the NetApp hardware management interface or run `sysctl -a` or check /var/log for firmware identification details
    Affected if The device is any of the NetApp H-series models listed (H300e, H300s, H500e, H500s, H700e, H700s) regardless of firmware version

A system is affected if it runs a Linux kernel within the specified version ranges AND uses NFS, or if it runs Fedora 35, or if it is a NetApp H-series device (all firmware versions).

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 4.4.269 / 4.9.269 / 4.14.233 or later
Fixed in 4.4.2694.9.2694.14.233
Interim mitigation

Apply the relevant Linux kernel security patches for this NFS subsystem vulnerability. Restrict NFS mount access to trusted users and systems to reduce the attack surface until patching can be completed.

Recommended fix High confidence

Linux Kernel 4.4.269+, 4.9.269+, 4.14.233+, or 4.19.191+ (or a later stable release such as 5.x)

  1. Check current kernel version: uname -r
  2. Update package repository metadata: dnf check-update (or apt-get update for Debian-based)
  3. Install the updated kernel package: dnf update kernel (or apt-get install linux-image-<version>)
  4. Verify the new kernel package is installed: rpm -qa | grep kernel
  5. Reboot the system to load the fixed kernel: systemctl reboot
  6. After reboot, verify the system is running the fixed kernel: uname -r
Caveat Kernel upgrades may require reboot and could affect proprietary kernel modules or drivers compiled against older kernel versions; test in staging if possible

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
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2021-4157 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