CVE-2026-31431 (Copy Fail) Detection Toolkit

Detection and analysis toolkit for CVE-2026-31431 "Copy Fail" - a critical Linux Local Privilege Escalation vulnerability affecting distributions from 2017 onwards.

Vulnerability Overview

CVE-2026-31431 exploits a logic flaw in the Linux kernel's algif_aead implementation, enabling reliable local privilege escalation through:

• Logic bug in kernel crypto API (algif_aead)
• Exploitation vector via AF_ALG socket interface and splice() system call
• 4-byte write primitive targeting page cache of setuid binaries
• 100% reliability - no race conditions or kernel-specific offsets required

Critical Impact Scenarios

• Container Escape: Privilege escalation from container to host root
• Multi-tenant Compromise: Cross-tenant privilege escalation in shared environments
• CI/CD Infrastructure: Malicious code execution in build pipelines
• Shared Development Systems: Any local user to root escalation

Detection Tools

1. Primary Detection Script (copy_fail_detect.py)

Comprehensive Python-based detection engine for active and forensic analysis.

Capabilities:

• AF_ALG socket enumeration and analysis
• Setuid binary integrity verification (disk vs memory comparison)
• Kernel crypto module status assessment
• System log analysis for exploitation indicators
• Process behavior analysis for crypto API abuse
• Authentication log correlation

Usage:

sudo sudo										# Privileged mode detects more artifacts
python3 copy_fail_detect.py                    	# Full system scan
python3 copy_fail_detect.py --monitor          	# Continuous monitoring mode

2. YARA Detection Rules (copy_fail_detection.yar)

Signature-based detection for file system and memory analysis.

Rule Coverage:

• CopyFail_Exploit_Python: Python exploit variants detection
• CopyFail_Exploit_Generic: Generic exploitation technique patterns
• CopyFail_InMemory_Artifacts: Runtime memory artifact detection
• CopyFail_Modified_SetUID: Modified setuid binary detection
• CopyFail_C_Implementation: C/C++ exploit implementation detection

Usage:

yara copy_fail_detection.yar /path/to/scan
yara copy_fail_detection.yar /proc/*/mem

3. Windows Environment Scanner (Copy-Fail-Windows-Detect.ps1)

PowerShell-based detection for Windows systems with WSL, Docker, or Linux VMs. ¡NOT FULLY TESTED!

Target Environments:

• Windows Subsystem for Linux (WSL) instances
• Docker containers running on Windows
• Windows Event Log analysis
• Cross-platform environment correlation

Usage:

.\Copy-Fail-Windows-Detect.ps1 -All
.\Copy-Fail-Windows-Detect.ps1 -WSL
.\Copy-Fail-Windows-Detect.ps1 -Docker

License and Legal Notice

This toolkit is provided for defensive cybersecurity purposes only. Usage must comply with applicable laws and organizational policies. Users are responsible for obtaining proper authorization before deployment in any environment.

References

• CVE Details: CVE-2026-31431
• Original Disclosure: https://copy.fail/
• Technical Analysis: Theori Security Research