dbcve.org
Linux KernelOperating system · Linux

CVE-2016-9644

HIGH · 7.8 CVSS v3.0 Published 2016-11-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
81/100
Remediation priority · High
No privileges

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
The __get_user_asm_ex macro in arch/x86/include/asm/uaccess.h in the Linux kernel 4.4.22 through 4.4.28 contains extended asm statements that are incompatible with the exception table, which allows local users to obtain root access on non-SMEP platforms via a crafted application. NOTE: this vulnerability exists because of incorrect backporting of the CVE-2016-9178 patch to older kernels.

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 privilege escalation vulnerability exists in the Linux kernel 4.4.22-4.4.28 in the x86 __get_user_asm_ex macro used for safe user-space memory access. The macro contains extended asm statements that are incompatible with the kernel's exception table handling, allowing local attackers to execute arbitrary code with root privileges on platforms lacking SMEP (Supervisor Mode Execution Prevention) protection. The bug resulted from incorrect backporting of an earlier CVE-2016-9178 fix.

MitigationUpgrade the kernel to version 4.4.29 or later, or apply the correct vendor patch for this vulnerability. Systems with SMEP enabled may have reduced exploitability but should still be patched.

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:= 4.4.22= 4.4.23= 4.4.24= 4.4.25= 4.4.26= 4.4.27= 4.4.28

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
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.0/AV:L/AC:L/PR:N/UI:R/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 installed kernel version
    Run `uname -r` or `cat /proc/version` to display the running kernel version
    Affected if The version displayed is 4.4.22, 4.4.23, 4.4.24, 4.4.25, 4.4.26, 4.4.27, or 4.4.28
  2. Confirm x86 architecture
    Run `uname -m` or check /proc/cpuinfo for 'GenuineIntel' or 'AuthenticAMD' and look for x86_64 or i686/i386 flags
    Affected if The system is running on an x86 (i386, i686, or x86_64) architecture
  3. Check if SMEP is enabled
    Check /proc/cpuinfo for the 'smep' flag in the flags line, or verify if 'nosmep' is absent in /proc/cmdline boot parameters
    Affected if The 'smep' flag is NOT present in cpuinfo AND 'nosmep' is not in boot cmdline (indicating SMEP is disabled or unavailable)

The system is affected if it runs a Linux kernel between 4.4.22 and 4.4.28 on an x86 platform without SMEP protection enabled.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade the kernel to version 4.4.29 or later, or apply the correct vendor patch for this vulnerability. Systems with SMEP enabled may have reduced exploitability but should still be patched.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2016-9644 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2016-9644 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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