InputPlumber Flaws Expose Linux Systems to UI Input Injection and DoS Attacks

Linux users – particularly those running SteamOS and gaming-focused distributions – are being urged to update immediately after security researchers uncovered serious authorization and input validation flaws in InputPlumber, a system service that runs with root privileges.

The vulnerabilities, tracked as CVE-2025-66005 and CVE-2025-14338, allow local attackers to inject keyboard input, leak sensitive information, or trigger denial-of-service conditions, all without proper authentication. The issues were disclosed following a coordinated investigation involving the openSUSE security team and the InputPlumber maintainers, with fixes now available in InputPlumber v0.69.0 and later.

What Is InputPlumber and Why It Matters

InputPlumber is a Linux utility designed to combine multiple physical input devices into virtual devices, commonly used in gaming setups and shipped as part of SteamOS. Under the hood, InputPlumber exposes a powerful D-Bus system service (org.shadowblip.InputManager) that runs with full root privileges.

That power, however, became its biggest weakness.

During a security review initiated as part of the openSUSE packaging process, researchers found that early versions of InputPlumber lacked any meaningful client authentication. Even after Polkit authorization was introduced, it was disabled by default and implemented in an unsafe way, leaving the door open for abuse by low-privileged local users.

The Core Security Issues Explained Simply

1. Broken or Missing Authentication

• Versions prior to v0.63.0 had no Polkit authorization at all.
• Later versions attempted to add Polkit but relied on a deprecated “unix-process” subject, vulnerable to race conditions.
• In practice, this meant any local user—including “nobody”—could access privileged D-Bus methods.

2. UI Input Injection via Virtual Keyboard

One exposed method allowed attackers to:

• Create a virtual keyboard device
• Inject keystrokes into active login screens or desktop sessions

This could potentially lead to arbitrary command execution in the context of the logged-in user, a serious risk on shared or multi-user systems.

3. Denial-of-Service and Information Leakage

Another vulnerable method allowed user-controlled file paths to be parsed as configuration files:

• Attackers could trigger memory exhaustion (e.g., reading /dev/zero)
• Or extract sensitive data, such as root’s .bash_history, via error messages

CVE Breakdown

• CVE-2025-66005
  Lack of authorization in InputPlumber versions before v0.63.0 allows DoS, information disclosure, and potential privilege escalation.
• CVE-2025-14338
  Polkit disabled by default and implemented with a race condition in versions before v0.69.0, leading to similar impact.

Fixes and Current Status

The good news: upstream developers responded quickly and responsibly.

In InputPlumber v0.69.0, the following improvements were implemented:

• Secure “system bus name” Polkit subject replaces the vulnerable authentication method
• Polkit authorization enabled by default
• Systemd service hardening applied to reduce blast radius
• Sensitive methods now require administrator privileges

However, some defense-in-depth gaps remain, particularly around fully replacing path-based inputs with validated file descriptors—a mitigation that is still under review.

SteamOS images version 3.7.20 have also been released with the fixed InputPlumber version.

Why This Matters Globally and for MEA

While this is a local vulnerability, its impact is global. Linux-based systems are widely used across:

• Technology companies
• Gaming and esports environments
• Developer workstations
• Education and innovation hubs

In the Middle East and Africa, where Linux adoption is growing across universities, startups, and government-backed digital initiatives, weaknesses in system services like InputPlumber can undermine trust in open-source platforms if left unpatched.

Organizations relying on Linux endpoints should treat local privilege abuse as a serious threat vector, not a theoretical one.

10 Recommended Actions for Security Teams

1. Immediately upgrade InputPlumber to v0.69.0 or later
2. Apply the latest SteamOS 3.7.20 images if applicable
3. Audit systems for exposed D-Bus system services
4. Enforce strict Polkit policies avoid relaxed admin rules
5. Monitor for unauthorized virtual input device creation
6. Harden systemd services using options like ProtectSystem=full
7. Limit local user access on shared Linux systems
8. Educate developers and admins on D-Bus security risks
9. Include local privilege abuse scenarios in threat models
10. Invest in continuous cybersecurity training and awareness

For expert support in Linux hardening, vulnerability management, and governance, consult Saintynet Cybersecurity:

Conclusion

The InputPlumber case is a reminder that local vulnerabilities still matter, especially when system services run as root and expose complex APIs like D-Bus. While upstream fixes have significantly reduced risk, organizations must stay vigilant patching promptly, hardening configurations, and treating endpoint security as a first-class priority.

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