CVE-2023-6931: Linux Kernel Privilege Escalation Flaw

CVE-2023-6931 Overview

A heap out-of-bounds write vulnerability exists in the Linux kernel's Performance Events (perf) system component that can be exploited to achieve local privilege escalation. The vulnerability occurs when a perf_event's read_size can overflow, leading to a heap out-of-bounds increment or write in the perf_read_group() function.

This is a critical memory corruption vulnerability that affects the kernel's performance monitoring subsystem, a privileged component used for hardware and software event profiling. Successful exploitation allows a local attacker with low privileges to potentially escalate their privileges to root level access.

Critical Impact

Local privilege escalation via heap out-of-bounds write in the Linux kernel Performance Events subsystem, potentially allowing complete system compromise.

Affected Products

• Linux Kernel (multiple versions prior to commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b)
• Debian Linux 10.0

Discovery Timeline

• December 19, 2023 - CVE-2023-6931 published to NVD
• February 13, 2025 - Last updated in NVD database

Technical Details for CVE-2023-6931

Vulnerability Analysis

The vulnerability resides in the Linux kernel's Performance Events subsystem, specifically within the perf_read_group() function. Performance Events is a kernel interface that provides access to hardware performance counters and software profiling events. The subsystem is commonly used by profiling tools such as perf and various performance monitoring utilities.

The core issue stems from an integer overflow condition affecting the read_size variable of a perf_event structure. When this overflow occurs, subsequent heap memory operations in perf_read_group() can write beyond the allocated buffer boundaries, corrupting adjacent heap metadata or data structures.

This type of heap out-of-bounds write vulnerability is particularly dangerous in kernel context because it can be leveraged to:

• Corrupt kernel data structures to gain elevated privileges
• Overwrite function pointers for arbitrary code execution in kernel mode
• Manipulate credentials structures to escalate from unprivileged user to root

Root Cause

The root cause is an integer overflow vulnerability (CWE-787: Out-of-bounds Write) in the calculation or handling of the read_size field within the Performance Events subsystem. The overflow occurs because proper bounds checking is not performed before the read_size value is used in memory operations, allowing an attacker to manipulate event configurations to trigger the overflow condition and cause out-of-bounds memory access.

Attack Vector

The attack requires local access to the target system with low-privilege user credentials. The attacker must be able to interact with the Performance Events subsystem through the perf_event_open() system call interface. By carefully crafting perf event configurations that trigger the integer overflow in read_size, the attacker can cause controlled heap corruption.

The exploitation flow typically involves:

1. Creating multiple perf event groups with specific configurations designed to overflow the read_size calculation
2. Triggering the perf_read_group() function through a read operation on the event file descriptor
3. Leveraging the out-of-bounds write to corrupt adjacent heap objects
4. Using heap manipulation techniques to achieve privilege escalation

While the attack complexity is considered high due to the precise heap layout manipulation required, the potential impact is severe as successful exploitation grants root-level access to the compromised system.

Detection Methods for CVE-2023-6931

Indicators of Compromise

• Unusual activity involving the perf_event_open() system call from unprivileged processes
• Kernel crash dumps or oops messages referencing perf_read_group or performance events subsystem
• Unexpected privilege escalation events in audit logs
• Signs of heap corruption in kernel memory debugging output

Detection Strategies

• Deploy SentinelOne Singularity XDR to monitor for suspicious local privilege escalation attempts and anomalous kernel behavior
• Enable kernel auditing rules to track perf_event_open() system calls from non-administrative users
• Monitor for processes unexpectedly gaining elevated privileges without corresponding sudo or authentication events
• Implement runtime kernel integrity monitoring to detect unauthorized modifications to kernel data structures

Monitoring Recommendations

• Configure SentinelOne agents to alert on behavioral indicators associated with kernel exploitation attempts
• Enable Linux audit framework (auditd) with rules targeting the performance events subsystem
• Deploy kernel memory corruption detection mechanisms such as KASAN (Kernel Address Sanitizer) in development and test environments
• Monitor system logs for kernel oops or panic events that may indicate exploitation attempts

How to Mitigate CVE-2023-6931

Immediate Actions Required

• Update Linux kernel to a version containing commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b or later
• Apply vendor-provided security patches for affected distributions (Debian LTS advisories available)
• Restrict access to the Performance Events subsystem for unprivileged users if not required
• Enable SentinelOne's kernel-level protection features to detect and prevent exploitation attempts

Patch Information

The Linux kernel maintainers have released a fix in commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b. This commit addresses the integer overflow condition in the Performance Events subsystem that allowed the heap out-of-bounds write. Organizations should update to kernel versions containing this fix.

For Debian-based systems, security updates are available through the Debian LTS announcements. Refer to the Debian LTS Security Announcements for specific package versions.

Additional resources:

• Linux Kernel Commit Update
• Kernel Dance Commit Reference

Workarounds

• Restrict perf events access by setting kernel.perf_event_paranoid to 2 or higher to limit unprivileged access
• Use kernel security modules (SELinux, AppArmor) to restrict access to the perf subsystem
• Monitor and limit user access to systems where patching is not immediately possible
• Consider temporarily disabling the perf subsystem if not required for operations

# Configuration example - Restrict perf events access
# Add to /etc/sysctl.conf or /etc/sysctl.d/99-security.conf

# Restrict unprivileged access to perf events
# Value 2 = disallow all performance measurements for unprivileged users
kernel.perf_event_paranoid = 2

# Apply changes immediately
sysctl -p