Horizon Alert
Summary of the vulnerability and why it matters
The Linux kernel's OverlayFS subsystem contains a weakness that allows a local user to escalate privileges. This is due to an issue in how the kernel handles user ID mapping when copying files between certain types of mounts. Specifically, a user can copy a file with special execution permissions from a restricted mount to an unrestricted one, retaining those permissions. This could enable an unprivileged user to gain administrative control over a system.
- Linux kernel OverlayFS subsystem
- Improper user ID mapping during file copy
- Local privilege escalation to root
Attack Path
How an attacker could exploit the issue
This vulnerability stems from a flaw in the Linux kernel's OverlayFS subsystem, specifically how it handles copying files with specific permissions across different mounted file systems. A local user can exploit this by copying a capable file from a "nosuid" mount to another mount. This interaction creates a privilege escalation opportunity on the affected system.
- Local user exposure
- Copy capable file from nosuid mount
- Gain elevated privileges
Live Threat
Current exploitation, exposure, and threat context
A vulnerability in the Linux kernel's OverlayFS subsystem allows for unauthorized access to the execution of setuid files with capabilities. This flaw stems from how a user copies a capable file from a nosuid mount into another mount, creating a uid mapping bug that enables local privilege escalation. The potential for damage is significant, impacting system integrity and data confidentiality. Organizations should consider this a high-priority issue requiring prompt attention.
- Likely attacker skill level: Low
- Required access or conditions: Local system access
- Business risk or urgency: High, potential privilege escalation
Priority actions
Operational Fix
Recommended remediation, mitigation, and detection steps
A vulnerability has been identified in the Linux kernel's OverlayFS subsystem that could allow a local user to escalate privileges. This issue arises from a flaw in how a user copies a file with specific capabilities from a "nosuid" mount point into another mount. This privilege escalation could impact system integrity and data security for organizations utilizing affected Linux kernel versions. The vulnerability has a high severity rating.
- Identify affected systems.
- Limit exposure and isolate risks.
- Apply vendor fixes and validate.
- Monitor for related activity.
