cfDr

cfDr — Ansible playbook for detecting and remediating CVE-2026-31431 (Copy Fail) - Linux kernel local privilege escalation vulnerability | Kitploit

Method	Can Root Bypass?	Coverage	Enterprise Linux Support
Module Blacklist	✅ Yes (via insmod)	Prevents modprobe loading	All versions
SELinux Policy	❌ NO (LSM layer)	Configured domains only	All versions (default)
systemd seccomp	❌ NO (syscall filter)	Configured services only	All versions
eBPF LSM	❌ NO (LSM layer)	System-wide (if configured)	RHEL 9+, Fedora 34+

┌─────────────────────────────────────────────────┐
│  Layer 1: Module Blacklist                      │
│  • Prevents modprobe algif_aead                 │
│  • Persists across reboots                      │
│  • CAN be bypassed by malicious root (insmod)   │
├─────────────────────────────────────────────────┤
│  Layer 2: SELinux Policy                        │
│  • Blocks AF_ALG socket() at syscall level      │
│  • Works even if module is loaded               │
│  • CANNOT be bypassed from userspace            │
│  • Covers user_t, unconfined_t (majority cases) │
└─────────────────────────────────────────────────┘

Result: If either layer fails, the other still protects

Flag Value	Mitigations Enabled	Use Case
1	Module Blacklist only	Minimal protection, systems without SELinux
2	SELinux only	SELinux-only environments
3	Module Blacklist + SELinux	RECOMMENDED default
5	Module Blacklist + seccomp	Non-SELinux with service hardening
7	Module Blacklist + SELinux + seccomp	Enhanced protection
15	All mitigations	Maximum protection (RHEL 9+ only)

Status	Condition	Action Required
VULNERABLE - Module loaded	Kernel >= 4.10, module exists AND loaded	IMMEDIATE - Actively exploitable
VULNERABLE - Module exists	Kernel >= 4.10, module exists, not loaded	HIGH - Can be loaded and exploited
MITIGATED - Module blacklisted	Blacklist detected	LOW - Monitor, apply additional layers
PROTECTED - Defense-in-depth	Blacklist + SELinux/seccomp/eBPF	NONE - Fully protected
NOT VULNERABLE - Old kernel	Kernel < 4.10	NONE - Predates vulnerability
NOT VULNERABLE - No module	algif_aead module not in kernel	NONE - Module not available

webserver1.example.com: VULNERABLE - Module exists and can be loaded
dbserver2.example.com: PROTECTED - Defense-in-depth (Module Blacklist + SELinux)
appserver3.example.com: NOT VULNERABLE - Module not available

cfDr/
├── roles/
│   └── cve_2026_31431/           # Main role
│       ├── tasks/
│       │   ├── main.yml           # Role orchestration
│       │   ├── assessment.yml     # Vulnerability detection
│       │   ├── remediation_module_blacklist.yml
│       │   ├── remediation_selinux.yml
│       │   ├── remediation_seccomp.yml
│       │   ├── remediation_ebpf.yml
│       │   ├── reporting.yml      # Status reporting
│       │   └── inventory_update.yml  # Inventory generation
│       ├── templates/             # Config file templates
│       ├── defaults/              # Default variables
│       └── handlers/              # Service restarts, etc.
├── quickstart.yml                 # Simplest usage
├── sample_playbook.yml            # Multiple examples
└── cve_2026_31431_playbook.yml   # Full-featured playbook

1. Pre-flight checks
   ↓
2. Gather system facts
   ↓
3. Detect kernel version
   ↓
4. Check module availability
   ↓
5. Check current load status
   ↓
6. Check existing mitigations
   ↓
7. Determine vulnerability status
   ↓
8. Flag vulnerable hosts
   ↓
9. Generate reports
   ↓
10. Create summary
   ↓
11. [Optional] Generate inventory

1-8. [Same as Assessment Mode]
   ↓
9. Apply Module Blacklist (if flag 1)
   • Unload module if loaded
   • Create blacklist config
   • Update initramfs/initrd
   • Verify blacklist works
   ↓
10. Apply SELinux Policy (if flag 2)
    • Install policy packages
    • Compile policy module
    • Install policy
    • Verify policy active
   ↓
11. Apply systemd seccomp (if flag 4)
    • Create drop-in files
    • Reload systemd
    • Restart services
    • Verify filters active
   ↓
12. Apply eBPF LSM (if flag 8)
    • Compile eBPF program
    • Load into kernel
    • Verify program attached
   ↓
13. Re-assess protection status
   ↓
14. Generate reports
   ↓
15. Create summary

Unloads algif_aead module if currently loaded (rmmod algif_aead)
Creates /etc/modprobe.d/blacklist-algif_aead-cve-2026-31431.conf:
```
blacklist algif_aead
install algif_aead /bin/true
```
Updates initramfs/initrd to persist across reboots:
- Debian/Ubuntu: update-initramfs -u
- RHEL/Fedora: dracut -f
Verifies module cannot be loaded via modprobe

inventory_output/
├── vulnerable_hosts.yml          # YAML inventory
├── vulnerable_hosts.ini          # INI inventory
├── group_vars_vulnerable_hosts.yml  # Group variables
└── host_vars/
    ├── host1.yml                 # Per-host details
    └── host2.yml

Service/Component	Function	Status
dm-crypt / LUKS	Full disk encryption	✅ Unaffected
IPsec / XFRM	VPN and encrypted networking	✅ Unaffected (validated)
kTLS	Kernel TLS implementation	✅ Unaffected
SSH	Secure shell connections	✅ Unaffected

Library	Usage	Status
OpenSSL (default)	SSL/TLS, certificates, general crypto	✅ Unaffected
GnuTLS (default)	TLS implementation	✅ Unaffected
NSS	Mozilla Network Security Services	✅ Unaffected
Kernel keyring	Kernel key management	✅ Unaffected

┌─────────────────────────────────────────────┐
│  Userspace Applications                     │
├─────────────────────────────────────────────┤
│  Standard Crypto Libraries                  │
│  (OpenSSL, GnuTLS, NSS)                    │
│  │                                          │
│  └─────> In-Kernel Crypto API ──────────┐  │
│           (Direct access)                │  │
├──────────────────────────────────────────┼──┤
│  AF_ALG Socket Interface (RARELY USED)   │  │
│  │                                       │  │
│  └─────> In-Kernel Crypto API ──────────┘  │
├─────────────────────────────────────────────┤
│  Kernel Crypto Subsystem                    │
│  (AES, SHA, AEAD algorithms)                │
└─────────────────────────────────────────────┘

Standard services bypass AF_ALG entirely

Flag	Mitigations	Impact on Standard Services
1	Module Blacklist	✅ Zero impact - AF_ALG not used
2	SELinux Policy	✅ Zero impact - Blocks unused syscall
3	Blacklist + SELinux	✅ Zero impact - RECOMMENDED
5	Blacklist + seccomp	✅ Zero impact - Per-service safe
7	Blacklist + SELinux + seccomp	✅ Zero impact - Defense-in-depth
15	All mitigations	✅ Zero impact - Maximum protection

# Test SSH connectivity
ssh localhost echo "SSH working"

# Test HTTPS (if web server running)
curl -k https://localhost

# Test LUKS encryption (if using encrypted volumes)
cryptsetup status /dev/mapper/luks-volume

# Test IPsec (if VPN configured)
ipsec status

# Test system services
systemctl status sshd
systemctl status httpd
systemctl status postgresql

# Check for any service failures
systemctl --failed

Your Environment	Recommendation	Reason
Standard RHEL servers	Deploy Flag 3 now	Zero impact, immediate protection
RHEL with custom crypto	Audit for AF_ALG usage first	Extremely unlikely, but verify
Development systems	Deploy Flag 3 now	Same as production
High-security environments	Deploy Flag 7 or 15	Maximum defense-in-depth

CVE-2026-31431 Summary Report
==========================================
Total hosts scanned: 50
Vulnerable hosts: 12

VULNERABLE HOSTS REQUIRING REMEDIATION:
web1.example.com, web2.example.com, db1.example.com, ...

DEFAULT RECOMMENDED MITIGATION: Flag 3
  - Module Blacklist (1) + SELinux (2) = Defense-in-depth
  - Module Blacklist alone can be bypassed by root (via insmod)
  - SELinux blocks syscall even if blacklist is bypassed
  - Covers user_t/unconfined_t (vast majority of scenarios)

# Apply to production in stages
# Stage 1: Web tier
ansible-playbook -i vulnerable_hosts/vulnerable_hosts.yml cve_2026_31431_playbook.yml \
  -e apply_remediation=true \
  --limit 'web*'

# Stage 2: Application tier
ansible-playbook -i vulnerable_hosts/vulnerable_hosts.yml cve_2026_31431_playbook.yml \
  -e apply_remediation=true \
  --limit 'app*'

# Stage 3: Database tier (most critical)
ansible-playbook -i vulnerable_hosts/vulnerable_hosts.yml cve_2026_31431_playbook.yml \
  -e apply_remediation=true \
  --limit 'db*'

# Immediate assessment and remediation
ansible-playbook -i inventory quickstart.yml -e apply_remediation=true -e mitigation_flags=3

# Re-verify all hosts
ansible-playbook -i inventory quickstart.yml

# Use enhanced protection (Flag 7: Blacklist + SELinux + seccomp)
ansible-playbook -i inventory quickstart.yml \
  -e apply_remediation=true \
  -e mitigation_flags=7

# Or customize per-host via inventory
# Edit generated host_vars/*.yml files to set custom flags
vim vulnerable_hosts/host_vars/web1.example.com.yml
# Change: recommended_mitigation_flags: 7

# Apply customized settings
ansible-playbook -i vulnerable_hosts/vulnerable_hosts.yml cve_2026_31431_playbook.yml \
  -e apply_remediation=true

# On remediated host:
sudo lsmod | grep algif_aead
# Should return nothing (module not loaded)

sudo modprobe algif_aead
# Should fail: "modprobe: ERROR: could not insert 'algif_aead'"

cat /etc/modprobe.d/blacklist-algif_aead-cve-2026-31431.conf
# Should show blacklist configuration

# Check SELinux policy
sudo semodule -l | grep cve_2026_31431
# Should show: cve_2026_31431_af_alg_deny

# Check seccomp (for services)
systemctl show httpd | grep RestrictAddressFamilies
# Should show: RestrictAddressFamilies=~AF_ALG

# Clone repository
git clone https://github.com/parmstro/cfDr.git
cd cfDr

# Step 1: Assess all hosts
ansible-playbook -i inventory quickstart.yml

# Step 2: Apply recommended mitigations to vulnerable hosts
ansible-playbook -i inventory quickstart.yml --limit vulnerable_hosts -e apply_remediation=true

# Assess with your inventory
ansible-playbook -i /path/to/your/inventory quickstart.yml

# Remediate vulnerable hosts
ansible-playbook -i /path/to/your/inventory quickstart.yml \
  --limit vulnerable_hosts \
  -e apply_remediation=true

# Scan and create inventory of vulnerable hosts
ansible-playbook -i inventory quickstart.yml -e generate_inventory=true

# Review generated files
ls inventory_output/

# Apply mitigations using generated inventory
ansible-playbook -i inventory_output/vulnerable_hosts.yml cve_2026_31431_playbook.yml \
  -e apply_remediation=true

# Module blacklist only
ansible-playbook quickstart.yml -e apply_remediation=true -e mitigation_flags=1

# SELinux only
ansible-playbook quickstart.yml -e apply_remediation=true -e mitigation_flags=2

# Module blacklist + SELinux (default recommended)
ansible-playbook quickstart.yml -e apply_remediation=true -e mitigation_flags=3

# Enhanced: Blacklist + SELinux + seccomp
ansible-playbook quickstart.yml -e apply_remediation=true -e mitigation_flags=7

# Maximum: All mitigations (RHEL 9+ only)
ansible-playbook quickstart.yml -e apply_remediation=true -e mitigation_flags=15

# Add additional domains to protect
selinux_denied_domains:
  - user_t
  - unconfined_t
  - httpd_t
  - postgresql_t
  - mysqld_t
  - custom_app_t        # Your custom domain
  - another_service_t

# Example 1: Assessment only
- hosts: all
  roles:
    - cve_2026_31431

# Example 2: Module blacklist only
- hosts: all
  vars:
    apply_remediation: true
    mitigation_flags: 1
  roles:
    - cve_2026_31431

# Example 3: Recommended (Blacklist + SELinux)
- hosts: all
  vars:
    apply_remediation: true
    mitigation_flags: 3
  roles:
    - cve_2026_31431

Email Alerts (Recommended):
- Log in to Red Hat Customer Portal
- Navigate to: Account Settings → Notifications
- Enable: "Security Advisories" and "Product Errata"
- Select: RHEL versions you manage
RSS Feeds:
- RHEL 7 Security: https://access.redhat.com/blogs/766093/feed
- RHEL 8 Security: https://access.redhat.com/blogs/1683903/feed
- RHEL 9 Security: https://access.redhat.com/blogs/5480361/feed
- All Security: https://access.redhat.com/security/data/oval/com.redhat.rhsa-all.xml

API Access:

# Check for kernel security updates
curl -H "Accept: application/json" \
  "https://access.redhat.com/labs/securitydataapi/cve/CVE-2026-31431.json"

Automated Monitoring:

# Install Red Hat Security Advisories plugin for yum
sudo yum install yum-plugin-security

# Check for security updates
sudo yum updateinfo list security

# Check specifically for kernel updates
sudo yum updateinfo list security kernel

# Subscribe to security announcements
# Visit: https://lists.fedoraproject.org/admin/lists/security-announce.lists.fedoraproject.org/

# Check for updates
sudo dnf check-update kernel

# View available security updates
sudo dnf updateinfo list security

# Subscribe to security announcements
# Visit: https://lists.ubuntu.com/mailman/listinfo/ubuntu-security-announce

# Check for security updates
sudo apt update
sudo apt list --upgradable | grep security

# Ubuntu Security Notices tool
sudo apt install ubuntu-security-tools
usn list --cve CVE-2026-31431

# Monitor kernel git for patches
git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

# Search for CVE-2026-31431 patches
git log --all --grep="CVE-2026-31431"

#!/bin/bash
# check-cve-2026-31431-patch.sh
# Monitors for CVE-2026-31431 kernel patches

DISTRO=$(grep ^ID= /etc/os-release | cut -d= -f2 | tr -d '"')

case $DISTRO in
  rhel|centos|rocky|alma)
    yum updateinfo list security kernel 2>/dev/null | grep -i CVE-2026-31431
    ;;
  fedora)
    dnf updateinfo list security kernel 2>/dev/null | grep -i CVE-2026-31431
    ;;
  ubuntu|debian)
    apt-get update -qq
    apt-cache show linux-image-$(uname -r) | grep CVE-2026-31431
    ;;
  sles|opensuse*)
    zypper info --cve CVE-2026-31431 kernel-default
    ;;
esac

# Check Red Hat Security Data API
curl -s "https://access.redhat.com/labs/securitydataapi/cve/CVE-2026-31431.json" | \
  jq -r '.affected_release[] | select(.package | startswith("kernel")) | 
         "\(.product_name): \(.advisory) - \(.package)"'

Verify patch availability:

# Check your distribution's update mechanism
sudo yum check-update kernel  # RHEL/CentOS/Fedora
sudo apt update && apt list --upgradable linux-image-*  # Ubuntu/Debian

Review release notes:
- Read vendor advisory for installation instructions
- Check for any known issues or prerequisites
- Verify kernel version numbers

Test in non-production:

# Apply kernel update to test systems first
sudo yum update kernel  # RHEL/CentOS/Fedora
sudo apt upgrade linux-image-*  # Ubuntu/Debian
sudo reboot

Verify patch effectiveness:

# After reboot, verify kernel version
uname -r

# Run cfDr assessment to confirm patch
ansible-playbook -i inventory quickstart.yml

Plan production rollout:
- Schedule maintenance windows
- Stage kernel updates
- Plan for service restarts/reboots

Remove temporary mitigations (optional):

# After patching, temporary mitigations can be removed
# However, defense-in-depth recommends keeping them

# If you choose to remove:
sudo rm /etc/modprobe.d/blacklist-algif_aead-cve-2026-31431.conf
sudo semodule -r cve_2026_31431_af_alg_deny  # SELinux policy
# Remove seccomp drop-in files
# Update initramfs/initrd

Most Popular

cfDr - Copy Fail Doctor

Repository

Table of Contents

Understanding CVE-2026-31431

What is Copy Fail?

Technical Details

Affected Systems

Why This Matters

Real-World Impact

Available Remediations

Understanding Protection Levels

Recommended Approach: Defense-in-Depth

Why Module Blacklist Alone Is Not Enough

Complete Protection Strategy

Mitigation Flag Reference

Coverage Gaps to Be Aware Of

Detection Methodology

How cfDr Detects Vulnerability

1. Kernel Version Check

2. Module Availability Check

3. Module Load Status

4. Active Socket Detection

5. Existing Mitigation Detection

6. Categorical Status Determination

Assessment Output

How cfDr Works

Architecture

Execution Flow

Assessment Mode (default)

Remediation Mode (apply_remediation=true)

Remediation Details

Module Blacklist (Flag 1)

SELinux Policy (Flag 2)

systemd seccomp (Flag 4)

eBPF LSM (Flag 8)

Inventory Generation

Impact on System Cryptography

Critical Finding: Standard RHEL Cryptography Is NOT Affected

What Is NOT Affected

Core System Services

Cryptographic Libraries

Critical Infrastructure

Why Standard Services Don't Use AF_ALG

What Might Be Affected (Rare Edge Cases)

1. OpenSSL with afalg Engine Explicitly Enabled

2. Custom Applications Using libkcapi

3. Hardware Crypto Offload Tools

Red Hat Official Position

Impact Assessment by Mitigation Flag

Verification After Remediation

Professional Security Community Consensus

Recommendation for Production Deployment

Summary

Recommended Workflow

Standard Enterprise Workflow

Step 1: Initial Assessment (Read-Only)

Step 2: Generate Vulnerability Inventory

Step 3: Test Remediation on Non-Production

Step 4: Production Remediation (Staged)

Step 5: Verification and Documentation

Emergency Response Workflow

Continuous Monitoring Workflow

Custom Mitigation Workflow

Verification Workflow

Quick Start

Simplest Usage

Using with Custom Inventory

Generating Vulnerability Inventory

Advanced Configuration

Customizing Mitigation Flags

Customizing SELinux Domains

Customizing seccomp Services

Custom Inventory Output Directory

Using Sample Playbook Templates

Requirements

Additional Resources

CVE Information and Analysis

Related Mitigation Projects

Remediation Mode (`apply_remediation=true`)