CVE-2026-46242: Bad Epoll Linux Kernel Privilege Escalation — Detection and Remediation Guide

---
title: Potential Bad Epoll Exploitation - Unexpected Root Shell Spawn
id: 8a4b3c2d-1e9f-4a7b-8c3d-2e1f4a5b6c7d
status: experimental
description: Detects suspicious root shell spawning from non-root parent processes, potentially indicating successful kernel exploitation like CVE-2026-46242 Bad Epoll.
references:
  - https://thehackernews.com/2026/07/new-bad-epoll-linux-kernel-flaw-lets.html
author: Security Arsenal
date: 2026/07/15
tags:
  - attack.privilege_escalation
  - attack.t1068
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    Image|endswith:
      - '/bin/sh'
      - '/bin/bash'
      - '/bin/zsh'
      - '/usr/bin/zsh'
    NewUID: 0
  filter:
    ParentUser:
      - 'root'
      - 'daemon'
      - 'systemd'
  condition: selection and not filter
falsepositives:
  - Legitimate sudo usage
  - System administration activities
  - Authorized privilege escalation tools
level: high
---
title: Suspicious Kernel Module Loading Activity
id: 9b5c4d3e-2f0a-5b8c-9d4e-3f2a5b6c7d8e
status: experimental
description: Detects unusual kernel module loading that may accompany kernel exploitation attempts or rootkit installation following CVE-2026-46242 exploitation.
references:
  - https://thehackernews.com/2026/07/new-bad-epoll-linux-kernel-flaw-lets.html
author: Security Arsenal
date: 2026/07/15
tags:
  - attack.persistence
  - attack.t1547.006
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    Image|endswith:
      - '/sbin/insmod'
      - '/sbin/modprobe'
      - '/sbin/rmmod'
    CommandLine|contains:
      - '/tmp/'
      - '/var/tmp/'
      - '/dev/shm/'
      - '/home/'
  filter_legitimate:
    User:
      - 'root'
  condition: selection and not filter_legitimate
falsepositives:
  - Authorized kernel module administration
  - Legitimate driver updates
level: medium
---
title: Suspicious Binary Execution from Temp Directories
id: 0c6d5e4f-3g1b-6c9d-0e5f-4g3b6c7d8e9f
status: experimental
description: Detects execution of binaries from temporary directories, which is common post-exploitation behavior following kernel privilege escalation like CVE-2026-46242.
references:
  - https://thehackernews.com/2026/07/new-bad-epoll-linux-kernel-flaw-lets.html
author: Security Arsenal
date: 2026/07/15
tags:
  - attack.execution
  - attack.t1059.004
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    Image|contains:
      - '/tmp/'
      - '/var/tmp/'
      - '/dev/shm/'
  filter_legitimate:
    Image|contains:
      - '/tmp/.font-unix/'
      - '/tmp/.ICE-unix/'
      - '/tmp/.X11-unix/'
    User:
      - 'root'
  condition: selection and not filter_legitimate
falsepositives:
  - Software package managers
  - Temporary build artifacts
level: medium

// Hunt for unexpected root shell spawning - potential kernel exploit success
Syslog
| where Facility in ("auth", "authpriv", "secure")
| where ProcessName =~ "su" or ProcessName =~ "sudo" or SyslogMessage contains "root"
| project TimeGenerated, HostName, ProcessName, SyslogMessage, SourceIP
| where SyslogMessage matches regex @"USER=root.*CMD="
| where not(SyslogMessage has anyof("pam_unix(sshd:session): session opened for user root", "sudo:.*: TTY=pts"))
| summarize count() by HostName, SourceIP, ProcessName, bin(TimeGenerated, 5m)
| where count_ > 0
| order by TimeGenerated desc
// Hunt for suspicious process execution patterns post-exploitation
DeviceProcessEvents
| where InitiatingProcessAccountName != "root" and AccountName == "root"
| where Timestamp > ago(24h)
| project Timestamp, DeviceName, AccountName, InitiatingProcessAccountName, FileName, CommandLine, ProcessIntegrityLevel
| where FileName in~ ("sh", "bash", "zsh", "python", "perl", "nc", "ncat", "socat")
| where CommandLine has anyof("/tmp/", "/dev/shm/", "curl ", "wget ")
| summarize count() by DeviceName, FileName, InitiatingProcessAccountName, bin(Timestamp, 1h)
| order by Timestamp desc
// Monitor for kernel panic or oops messages that may indicate exploit attempts
Syslog
| where SyslogMessage has_any ("kernel: ", "general protection fault", "kernel BUG", "kernel panic", "oops")
| where SyslogMessage has "epoll"
| project TimeGenerated, HostName, SeverityLevel, SyslogMessage
| order by TimeGenerated desc

-- Hunt for processes with unexpected root privileges
SELECT Pid, Name, CommandLine, Exe, Username, Uid, Gid, StartTime, Cwd
FROM pslist()
WHERE Uid = 0
  AND Name IN ("sh", "bash", "zsh", "python", "perl", "ruby", "nc", "ncat", "socat")
  AND (Cwd =~ "^/tmp/" OR Cwd =~ "^/var/tmp/" OR Cwd =~ "^/dev/shm/")
-- Check for suspicious kernel modules loaded recently
SELECT Name, Size, UsedBy, Tainted, TimeStamp
FROM kernel_modules()
WHERE Name =~ "^evil" 
   OR Name =~ "^rootkit"
   OR TimeStamp > now() - 24h
-- Identify recently modified binaries in common execution paths
SELECT FullPath, Size, Mode, Mtime, Atime, Btime, Hash
FROM glob(globs="/*
        /usr/bin/*, /usr/sbin/*, /usr/local/bin/*")
WHERE Mtime > now() - 48h
  AND Mode.ModeString =~ "^-rwxr-xr-x"
ORDER BY Mtime DESC
LIMIT 50

#!/bin/bash
# CVE-2026-46242 Bad Epoll - Kernel Patch Verification Script
# Run as root to check patch status across the environment

echo "=== CVE-2026-46242 Bad Epoll Remediation Check ==="
echo "Checking kernel version and patch status..."

# Get current kernel version
KERNEL_VERSION=$(uname -r)
echo "Current kernel version: $KERNEL_VERSION"

# Check for vulnerable kernel versions based on distribution
if [ -f /etc/os-release ]; then
    . /etc/os-release
    echo "Operating System: $PRETTY_NAME"
fi

# Function to check if kernel needs update
check_kernel_status() {
    # For RHEL/CentOS/Fedora
    if command -v rpm &> /dev/null; then
        INSTALLED_KERNEL=$(rpm -q kernel | tail -n 1 | sed 's/kernel-//')
        AVAILABLE_KERNEL=$(rpm -q --queryformat='%{VERSION}-%{RELEASE}.%{ARCH}\n' kernel 2>/dev/null | tail -n 1)
        if [ "$INSTALLED_KERNEL" != "$AVAILABLE_KERNEL" ]; then
            echo "WARNING: Kernel update available: $AVAILABLE_KERNEL"
            echo "Current installed: $INSTALLED_KERNEL"
            return 1
        fi
    fi
    
    # For Debian/Ubuntu
    if command -v dpkg &> /dev/null; then
        LATEST_KERNEL=$(dpkg -l | grep '^ii.*linux-image-[0-9]' | awk '{print $3}' | sort -V | tail -n 1)
        RUNNING_KERNEL=$(uname -r | sed 's/-generic//')
        if ! dpkg -l | grep -q "linux-image-$RUNNING_KERNEL"; then
            echo "WARNING: Running kernel may not be the latest installed"
            echo "Latest installed package version: $LATEST_KERNEL"
            return 1
        fi
    fi
    
    # Check Android (if applicable)
    if [ -f /system/build.prop ]; then
        ANDROID_PATCH_LEVEL=$(grep ro.build.version.security_patch /system/build.prop | cut -d= -f2)
        echo "Android security patch level: $ANDROID_PATCH_LEVEL"
        # Android patch for CVE-2026-46242 should be in July 2026 security patch
        if [[ "$ANDROID_PATCH_LEVEL" < "2026-07" ]]; then
            echo "WARNING: Android device vulnerable - security patch level predates July 2026"
            return 1
        fi
    fi
    
    return 0
}

# Run kernel status check
if ! check_kernel_status; then
    echo ""
    echo "ACTION REQUIRED: Kernel update detected"
    echo "To apply the update:"
    echo "  - RHEL/CentOS: yum update kernel && reboot"
    echo "  - Debian/Ubuntu: apt update && apt upgrade linux-image-generic && reboot"
    echo "  - Android: Apply latest security update via system settings"
    echo ""
    echo "After reboot, verify the new kernel is active:"
    echo "  uname -r"
    exit 1
else
    echo "Kernel appears to be patched against CVE-2026-46242"
    exit 0
fi