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Linux KernelOperating system · Linux

CVE-2021-3640

HIGH · 7.0 CVSS v3.1 Published 2022-03-03
Fix available
A fix is available. Upgrade to 4.4.293 / 4.9.291 or later.
See remediation →
72/100
Remediation priority · Elevated
Public exploit Zero-click Patch available

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 use-after-free in function sco_sock_sendmsg() of the Linux kernel HCI subsystem was found in the way user calls ioct UFFDIO_REGISTER or other way triggers race condition of the call sco_conn_del() together with the call sco_sock_sendmsg() with the expected controllable faulting memory page. A privileged local user could use this flaw to crash the system or escalate their 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
How this class of weakness works · CWE-362

Two operations that should be atomic can interleave, so an attacker who wins a narrow timing window reaches an inconsistent, exploitable state. These bugs are subtle and easy to miss in review. Fixing them properly means correct locking or atomic operations around the shared resource.

General guidance for the race condition class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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:< 4.4.293>= 4.5, < 4.9.291>= 4.10, < 4.14.256>= 4.15, < 4.19.218>= 4.20, < 5.4.160>= 5.5.0, < 5.10.80>= 5.11, < 5.14.19>= 5.15, < 5.15.3
Debian LinuxOperating system
Affected:= 9.0
FedoraOperating system
Affected:= 34
Ubuntu LinuxOperating system
Affected:= 14.04= 16.04= 18.04= 20.04= 21.10
H300s FirmwareOperating system
Affected:all versions
H700s FirmwareOperating system
Affected:all versions
H300e FirmwareOperating system
Affected:all versions
H500e 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
Local
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

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 4.4.293 / 4.9.291 / 4.14.256 or later
Fixed in 4.4.2934.9.2914.14.256
Vendor patch bugzilla.redhat.com →
Recommended fix High confidence

Linux Kernel 4.4.293, 4.9.291, 4.14.256, 4.19.218 or later stable releases; for newer kernels (5.x, 6.x) the fix is included in upstream

  1. 1. Identify the currently running kernel version using `uname -r`
  2. 2. For Red Hat/CentOS systems: upgrade kernel to version 4.4.293 or later (for 4.4.x), 4.9.291 or later (for 4.9.x), 4.14.256 or later (for 4.14.x), or 4.19.218 or later (for 4.19.x) using `yum update kernel` or `dnf update kernel`
  3. 3. For Debian/Ubuntu systems: run `apt-get update && apt-get dist-upgrade` to receive kernel updates, or install specific fixed kernel packages
  4. 4. For Fedora 34: run `dnf update kernel` to get the patched kernel
  5. 5. Reboot the system to load the fixed kernel using `reboot`
  6. 6. Verify the kernel version after reboot using `uname -r` to confirm the fix is applied
  7. 7. For affected H300s/H700s/H300e/H500e firmware: contact the vendor (NetApp) for firmware updates as mentioned in security.netapp.com reference
Caveat Standard kernel upgrade risks apply - ensure compatibility with existing system drivers and modules before rebooting

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,950. Get the upgrade done

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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-2021-3640 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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