CVE-2023-1249: Linux Kernel Use-After-Free Vulnerability

CVE-2023-1249 Overview

A use-after-free flaw was found in the Linux kernel's core dump subsystem. This vulnerability allows a local user to crash the system, resulting in a denial of service condition. The flaw specifically affects systems where patch 390031c94211 ("coredump: Use the vma snapshot in fill_files_note") has not been applied.

Critical Impact

Local users can exploit this use-after-free vulnerability in the core dump subsystem to cause system crashes, leading to denial of service conditions on affected Linux systems.

Affected Products

• Linux Kernel (all vulnerable versions without patch 390031c94211)
• CentOS Stream 9 (identified as missing the security fix)
• Linux-based systems utilizing the affected core dump subsystem

Discovery Timeline

• 2023-03-23 - CVE-2023-1249 published to NVD
• 2025-03-19 - Last updated in NVD database

Technical Details for CVE-2023-1249

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue 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 core dump subsystem, this flaw exists within the fill_files_note function responsible for generating the file mappings section of core dump files.

The vulnerability requires local access to exploit, meaning an attacker must have some level of access to the target system. No user interaction is required for exploitation, and the attacker only needs low-level privileges to trigger the condition. While the vulnerability does not impact data confidentiality or integrity, it poses a significant availability risk as successful exploitation results in a complete system crash.

Root Cause

The root cause of this vulnerability lies in improper memory management within the core dump generation process. During core dump creation, the kernel captures information about the process's virtual memory areas (VMAs). The vulnerability occurs because the code accesses VMA structures that may have been freed or modified during the core dump operation.

The fix, implemented in patch 390031c94211, addresses this by using a VMA snapshot mechanism in the fill_files_note function, ensuring that the VMA data being accessed remains valid throughout the core dump generation process.

Attack Vector

The attack vector is local, requiring the attacker to have existing access to the system with low-level user privileges. An attacker can exploit this vulnerability by triggering a core dump under specific conditions that cause a race condition or memory access timing issue in the VMA handling code.

The exploitation involves forcing the kernel to generate a core dump while simultaneously manipulating memory regions, creating a window where the kernel attempts to access freed VMA structures. This can be achieved through various means, including:

• Triggering a segmentation fault in a specifically crafted process
• Manipulating process memory mappings during core dump generation
• Exploiting timing windows in multi-threaded applications

The vulnerability mechanism can be understood through the interaction between core dump generation and VMA management. When a process crashes and a core dump is initiated, the kernel iterates through the process's VMAs to record file mapping information. Without the protective snapshot mechanism, these VMAs can be freed by concurrent operations, leaving dangling pointers that when accessed cause a use-after-free condition leading to system crash.

For detailed technical analysis, refer to the Kernel Patch Discussion Thread.

Detection Methods for CVE-2023-1249

Indicators of Compromise

• Unexpected system crashes or kernel panics, particularly during process termination
• Kernel log messages referencing use-after-free conditions in core dump related functions
• Abnormal system reboots correlated with core dump generation activities
• Crash dump files indicating memory corruption in fill_files_note or related VMA handling code

Detection Strategies

• Monitor kernel logs for use-after-free warnings or errors related to the core dump subsystem
• Implement kernel oops/panic monitoring to detect crashes potentially related to this vulnerability
• Use kernel address sanitizer (KASAN) in development environments to identify use-after-free conditions
• Deploy SentinelOne Singularity platform for real-time kernel behavior monitoring and anomaly detection

Monitoring Recommendations

• Enable comprehensive kernel logging to capture core dump subsystem activities
• Configure crash reporting mechanisms to analyze kernel panics for signs of this vulnerability
• Implement system stability monitoring to track unexpected reboot patterns
• Use SentinelOne's kernel-level visibility to detect suspicious memory access patterns indicative of exploitation attempts

How to Mitigate CVE-2023-1249

Immediate Actions Required

• Verify whether patch 390031c94211 has been applied to your kernel installation
• Update the Linux kernel to a version that includes the security fix
• Review the Packet Storm Security Advisory for distribution-specific guidance
• Prioritize patching for systems where local user access is granted to untrusted users

Patch Information

The vulnerability is addressed by kernel patch 390031c94211 titled "coredump: Use the vma snapshot in fill_files_note". This patch modifies the core dump generation process to use a snapshot of the VMA structures rather than accessing them directly, preventing the use-after-free condition.

Organizations running CentOS Stream 9 should pay particular attention to this vulnerability, as indicated by the security advisory noting the missing fix. Administrators should verify their kernel version includes this patch and update accordingly.

For patch details and implementation, review the Kernel Patch Discussion Thread.

Workarounds

• Restrict local user access to minimize the attack surface until patching is complete
• Consider disabling core dump generation on critical systems as a temporary measure (note: this may impact debugging capabilities)
• Implement strict process isolation using containers or namespaces to limit the impact of potential exploitation
• Monitor systems for crash patterns that may indicate exploitation attempts

# Configuration example: Temporarily disable core dumps system-wide
# Add to /etc/security/limits.conf
* hard core 0

# Or set via sysctl
sysctl -w kernel.core_pattern="|/bin/false"

# Verify patch status by checking kernel version
uname -r
# Check if the specific patch is included in your kernel
zcat /proc/config.gz | grep -i coredump