Research Context
In the world of Linux system security, Race Conditions have always been one of the most dangerous and fascinating vulnerability classes to exploit. Today, I want to discuss my latest Proof of Concept (PoC) published on GitHub: CVE-2025-6019 - udisks2 XFS Resize TOCTOU Privilege Escalation.
In this project, I demonstrate how a “Time-of-Check to Time-of-Use” (TOCTOU) vulnerability during the resizing of XFS filesystems by the udisks2 service can be implemented as a PoC to achieve Local Privilege Escalation (LPE).
🔍 The Core of the Vulnerability
udisks2 is a widely used D-Bus service that automates disk management tasks. The heart of this vulnerability lies in how udisks2 handles temporary mount points (/tmp/blockdev.XXXXXX) when processing XFS resize requests. The critical issue is this: there is a narrow time window between when the system creates the directory and mounts the filesystem, and when it applies the necessary security restrictions (like the nosuid flag). If we can place and execute an SUID binary inside this temporary directory within that exact window, we gain system-level execution
🛠️ Exploitation Steps (How It Works)
In my repository (🔗 JM00NJ/CVE-2025-6019), I have broken down the exploitation process into three main stages:
Evaluating Polkit Access Controls (bypass.py): Standard users (especially in remote sessions like SSH or Docker) are usually restricted from interacting with udisks2 by Polkit. The first step involves spoofing a local session (seat0) via ~/.pam_environment to bypass these restrictions.
PoC Development and Image Structure (weapon.py): Using the Protofile feature of mkfs.xfs, we can craft a specialized XFS image. This allows us to bake an SUID binary (pwnbash) directly into the image’s metadata without requiring root privileges during the creation phase.
Triggering the Race (trigger.sh): We flood the udisks2 daemon with D-Bus resize requests. As the system continuously creates temporary mount points under /tmp, we monitor the directory. If we manage to execute pwnbash before the nosuid flag is fully applied by the system, we win the race (Race Condition) and escalate our privileges.
🎯 Target Environments
This PoC is designed to be architecture-agnostic (working on x86, x64, ARM, etc.) and targets any Linux system with udisks2 (with D-Bus access enabled) and xfsprogs installed. The exploit has been successfully tested on openSUSE Leap 15.6 (Kernel 6.4.0).
💡 Conclusion and Source Code
TOCTOU vulnerabilities serve as a stark reminder of how careful modern operating systems must be when managing temporary files and directories. A seemingly simple logic flaw, combined with precise timing, can lead to full system compromise.
Security researchers, Blue Team members, and exploit development enthusiasts can find the full project and PoC code on my GitHub profile:
🔗 GitHub Repo: JM00NJ/CVE-2025-6019-udisks2-XFS-Resize-TOCTOU-Privilege-Escalation
⚠️ Legal Disclaimer
This project is created for educational purposes and security research only. Unauthorized access to computer systems is illegal. The author is not responsible for any misuse of this tool. Operating this tool on networks you do not own is strictly prohibited.