Linux KernelOperating system · Linux
CVE-2021-3428
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 · uneditedA flaw was found in the Linux kernel. A denial of service problem is identified if an extent tree is corrupted in a crafted ext4 filesystem in fs/ext4/extents.c in ext4_es_cache_extent. Fabricating an integer overflow, A local attacker with a special user privilege may cause a system crash problem which can lead to an availability threat.
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 confidenceA local privilege escalation vulnerability exists in the Linux kernel's ext4 filesystem driver. The flaw is in ext4_es_cache_extent in fs/ext4/extents.c, where an integer overflow occurs when handling a corrupted extent tree in a crafted ext4 filesystem. An attacker with special user privileges can trigger this to cause a denial of service via system crash.
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
< 5.9.0CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Check the running kernel versionRun 'uname -r' or 'cat /proc/version' to obtain the kernel version numberAffected if The version is earlier than 5.9.0 (e.g., 5.8.x, 5.4.x, 4.x.x)
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Verify ext4 filesystem support is presentCheck if the ext4 module is loaded ('lsmod | grep ext4') or if ext4 support is compiled into the kernel ('cat /proc/filesystems | grep ext4')Affected if ext4 filesystem support is available in the kernel
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Determine if the user can mount filesystemsCheck for CAP_SYS_ADMIN capability or root privileges using 'capsh --print' or 'id' command. The vulnerability requires privileges to mount a crafted ext4 filesystemAffected if The user has CAP_SYS_ADMIN capability or root access, allowing them to mount arbitrary ext4 filesystems
You are affected if your kernel version is below 5.9.0 AND you have users with privileges to mount ext4 filesystems (CAP_SYS_ADMIN or root).
Generated from the published advisory. Verify against your own configuration.
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 · scoped5.9.0
Apply the upstream kernel patch addressing the integer overflow in ext4_es_cache_extent. Additionally, restrict the ability to mount untrusted ext4 filesystems and monitor for unusual filesystem operations from privileged accounts.
Linux Kernel 5.9.0 or later stable releases
- Upgrade Linux kernel to version 5.9.0 or later to remediate the integer overflow vulnerability in ext4_es_cache_extent
- After kernel upgrade, reboot the system to load the fixed kernel
- Verify the running kernel version with 'uname -r' to confirm the fix is applied
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
- Testing16.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,576.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-3428 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-3428 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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