CVE-2020-14351: Linux Kernel Use-After-Free Vulnerability

CVE-2020-14351 Overview

A use-after-free memory flaw was discovered in the Linux kernel's perf subsystem. This vulnerability allows a local attacker with permission to monitor perf events to corrupt memory and potentially escalate privileges on the affected system. The perf subsystem is a critical component used for performance monitoring and profiling in Linux systems, making this vulnerability particularly concerning for multi-user environments and shared systems.

Critical Impact

Local attackers with perf monitoring permissions can exploit this use-after-free condition to corrupt kernel memory, potentially achieving privilege escalation and compromising system confidentiality, integrity, and availability.

Affected Products

• Linux Kernel (multiple versions)
• Red Hat Enterprise Linux 7.0
• Red Hat Enterprise Linux 8.0
• Debian Linux 9.0

Discovery Timeline

• 2020-12-03 - CVE-2020-14351 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-14351

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of the Linux kernel's perf subsystem, this flaw allows for dangerous memory operations that can lead to system compromise.

The perf subsystem provides performance monitoring capabilities through hardware and software counters. A local attacker with permissions to monitor perf events can trigger a condition where freed memory is accessed and manipulated. This memory corruption can be leveraged to modify kernel data structures, potentially allowing the attacker to escalate their privileges to root level access.

The vulnerability requires local access and appropriate permissions to interact with the perf subsystem, which somewhat limits the attack surface. However, in multi-tenant environments or systems where unprivileged users have access to perf monitoring capabilities, this represents a significant security risk.

Root Cause

The root cause of this vulnerability lies in improper memory management within the perf subsystem's event handling code. When perf events are created, modified, or destroyed, the associated memory structures must be carefully managed to prevent use-after-free conditions. In this case, a race condition or improper reference counting allows a memory region to be freed while still being referenced by other parts of the perf subsystem code path.

Attack Vector

The attack vector is local, requiring the attacker to have authenticated access to the system and permissions to monitor perf events. The exploitation typically involves:

1. Initial Access: The attacker gains local access to a vulnerable Linux system
2. Permission Check: The attacker must have permission to use the perf subsystem (often controlled by perf_event_paranoid sysctl)
3. Trigger Condition: The attacker creates and manipulates perf events to trigger the use-after-free condition
4. Memory Corruption: Once triggered, the freed memory can be reallocated and populated with attacker-controlled data
5. Privilege Escalation: By carefully controlling the corrupted memory contents, the attacker can modify kernel structures to gain elevated privileges

The vulnerability mechanism involves the perf subsystem's memory management routines. When perf events are monitored and freed, a race condition can occur that leaves dangling pointers accessible. For detailed technical information, see the Red Hat Bug Report #1862849.

Detection Methods for CVE-2020-14351

Indicators of Compromise

• Unusual perf event activity from non-administrative users
• Kernel crash logs (oops/panics) referencing the perf subsystem
• Unexpected privilege escalation events following perf-related activity
• Memory corruption signatures in kernel logs

Detection Strategies

• Monitor perf_event_open system calls for anomalous patterns
• Implement audit rules for perf subsystem access using auditd
• Deploy kernel integrity monitoring to detect unauthorized modifications
• Use SentinelOne Singularity Platform for real-time kernel-level threat detection

Monitoring Recommendations

• Enable kernel logging for perf subsystem events
• Configure perf_event_paranoid to restrict access to trusted users only
• Implement centralized log collection for kernel messages across affected systems
• Deploy endpoint detection solutions capable of monitoring kernel-level activity

How to Mitigate CVE-2020-14351

Immediate Actions Required

• Update the Linux kernel to a patched version as soon as available
• Restrict access to the perf subsystem by setting kernel.perf_event_paranoid=3
• Review and audit users with perf monitoring permissions
• Monitor systems for signs of exploitation attempts

Patch Information

Security patches addressing this vulnerability have been released by major Linux distribution vendors. Consult the following resources for patch details:

• Red Hat Bug Report #1862849 - Contains tracking information and patch references
• Debian LTS Advisory December 2020 - Debian security update information

System administrators should apply kernel updates from their respective distribution repositories and reboot systems to ensure the patched kernel is loaded.

Workarounds

• Set kernel.perf_event_paranoid=3 to disable perf events for unprivileged users
• Remove perf monitoring capabilities from non-essential user accounts
• Use Linux Security Modules (SELinux/AppArmor) to restrict perf subsystem access
• Consider disabling the perf subsystem entirely if not required for operations

# Configuration example
# Restrict perf event access to root only
echo 'kernel.perf_event_paranoid=3' >> /etc/sysctl.conf
sysctl -p

# Verify the setting
sysctl kernel.perf_event_paranoid