Linux Kernel Copy-on-Write Race Condition Local Privilege Escalation (Dirty COW, CVE-2016-5195)
Executive & SecOps Summary
SECOPS ASSESSMENTAll Linux distributions and Android systems running Linux kernel versions 2.x through 4.x before 4.8.3
A local attacker can exploit a race condition to write to read-only memory mappings, gaining root privileges on the target system
Apply the latest kernel security patches provided by your OS vendor and reboot the system
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Update your Linux kernel to the latest patched version using your distribution's package manager.
# For RHEL / CentOS systems
sudo yum update kernel -y
sudo reboot
# For Debian / Ubuntu systems
sudo apt-get update && sudo apt-get install --only-upgrade linux-image-generic -y
sudo reboot2. Temporary Workaround & Hardening Configuration
If an immediate reboot is not feasible, restrict local shell access for untrusted users and monitor system calls using auditd.
# Monitor suspicious memory mapping and write activities via auditd
sudo auditctl -a always,exit -F arch=b64 -S mmap,mprotect -k memory_abuse3. Log Audit & IoC Verification Commands
Verify the current running kernel version to determine if the system is running a vulnerable kernel.
# Check current kernel release
uname -r
# Simple version check helper
CURRENT_KERNEL=$(uname -r | cut -d'-' -f1)
PATCHED_VERSION='4.8.3'
if [ '$(printf '%s\
' '$PATCHED_VERSION' '$CURRENT_KERNEL' | sort -V | head -n1)' = '$PATCHED_VERSION' ]; then
echo 'Status: SECURE (Kernel is patched or newer)'
else
echo 'Status: VULNERABLE (Kernel update required)'
fiBlock Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability, widely known as 'Dirty COW', is a race condition found in the way the Linux kernel's memory subsystem handled copy-on-write (COW) breakage of private read-only memory mappings in mm/gup.c. The root cause lies in a synchronization flaw when the kernel processes write access to a read-only page, allowing the page table state to be manipulated during the COW process.
2. Exploitation Mechanics & Attack Scenario
An attacker spawns two competing threads: one that continuously calls madvise(MADV_DONTNEED) on a memory-mapped read-only file, and another that writes to the same memory space using write or /proc/self/mem. Due to the lack of proper locking, the kernel can be raced into discarding the newly created private copy of the page and writing directly to the original read-only physical page, allowing modification of critical system files like /etc/passwd.
3. Infrastructure & Business Impact
Successful exploitation allows any local user with minimal privileges to obtain full root access. In multi-tenant environments, cloud infrastructures, or containerized environments, this can lead to complete host compromise and container escape. This vulnerability has been actively exploited in the wild.
Official Vendor Advisories & References
Race condition in mm/gup.c in the Linux kernel 2.x through 4.x before 4.8.3 allows local users to gain privileges by leveraging incorrect handling of a copy-on-write (COW) feature to write to a read-only memory mapping, as exploited in the wild in October 2016, aka "Dirty COW."
Frequently Asked SecOps Questions (CVE-2016-5195)
FAQQ1. How critical is CVE-2016-5195 and is it actively exploited in the wild?
CVE-2016-5195 is rated CVSS 7.0 (HIGH) with a 30-day EPSS exploitation probability of 83.5%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2016-5195?
Primary impacted vendors include linux across linux_kernel. Scope summary: Linux Kernel 2.x through 4.x before 4.8.3
Q3. What temporary mitigations or workarounds exist for CVE-2016-5195 before patching?
[Mitigation] Apply the latest kernel security patches provided by your OS vendor and reboot the system Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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