CVE-2021-3982 in gnome-shell
Summary
by MITRE • 04/29/2022
Linux distributions using CAP_SYS_NICE for gnome-shell may be exposed to a privilege escalation issue. An attacker, with low privilege permissions, may take advantage of the way CAP_SYS_NICE is currently implemented and eventually load code to increase its process scheduler priority leading to possible DoS of other services running in the same machine.
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Analysis
by VulDB Data Team • 08/23/2025
The vulnerability described in CVE-2021-3982 represents a significant privilege escalation risk within Linux systems that employ the CAP_SYS_NICE capability for the gnome-shell process. This flaw exists in the implementation of the Linux capability system where the CAP_SYS_NICE capability allows processes to raise process priorities and modify scheduling policies. When gnome-shell runs with this capability, it creates an attack surface that malicious users can exploit to elevate their privileges and potentially disrupt system operations.
The technical implementation of this vulnerability stems from how the Linux kernel handles the CAP_SYS_NICE capability, which should normally be restricted to prevent unauthorized process priority manipulation. However, the specific implementation in affected Linux distributions allows processes with this capability to load code that can increase their scheduling priority beyond normal limits. This creates a path for attackers to potentially cause denial of service conditions by manipulating the scheduler to starve other critical system processes of CPU resources, effectively compromising system stability and availability.
From an operational impact perspective, this vulnerability poses serious risks to desktop environments where gnome-shell operates with elevated privileges. Attackers can leverage this capability to perform privilege escalation attacks that may allow them to gain root access or at minimum disrupt system services. The potential for denial of service attacks extends beyond simple process manipulation to include resource exhaustion and system instability that can affect multiple users and services running on the same machine. The vulnerability particularly impacts systems where desktop environments are configured with overly permissive capabilities, creating a persistent threat vector that can be exploited repeatedly.
The mitigation strategies for this vulnerability primarily involve removing or restricting the CAP_SYS_NICE capability from gnome-shell processes, ensuring that desktop environments operate with the minimum required privileges. System administrators should implement capability restrictions through systemd service configurations and review existing security policies to prevent unnecessary privilege escalation. Additionally, regular updates to Linux distributions and kernel versions that address this specific capability implementation issue are essential. Organizations should also consider implementing monitoring solutions to detect unusual process priority changes that might indicate exploitation attempts. This vulnerability aligns with CWE-276, which addresses improper privilege management, and relates to ATT&CK technique T1068, which involves privilege escalation through local exploitation of system vulnerabilities. The fundamental issue demonstrates how capability-based security models can introduce unintended access paths when not properly configured and enforced across system components.