CVE-2023-6176: Linux Kernel Privilege Escalation Flaw

CVE-2023-6176 Overview

A null pointer dereference vulnerability has been identified in the Linux kernel API for the cryptographic algorithm scatterwalk functionality. This flaw occurs when a user constructs a malicious packet with specific socket configuration, which could allow a local user to crash the system or potentially escalate their privileges on the system.

Critical Impact

Local attackers with low privileges can exploit this vulnerability to cause system denial of service (crash) or potentially escalate privileges through the cryptographic scatterwalk API.

Affected Products

• Linux Kernel (all vulnerable versions)
• Red Hat Enterprise Linux 8.0
• Red Hat Enterprise Linux 9.0

Discovery Timeline

• November 16, 2023 - CVE-2023-6176 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-6176

Vulnerability Analysis

This vulnerability is classified as CWE-476 (NULL Pointer Dereference) and affects the Linux kernel's cryptographic subsystem. The flaw exists within the scatterwalk functionality, which is used for handling scatter-gather lists in cryptographic operations.

The vulnerability can be triggered when a local user with low-level access constructs a specially crafted packet combined with specific socket configurations. When the kernel processes this malicious input, it attempts to dereference a null pointer within the cryptographic API, leading to a kernel panic or potential memory corruption that could be leveraged for privilege escalation.

While the attack requires local access and specific conditions to exploit successfully, the impact on system availability is significant as it can crash the entire system.

Root Cause

The root cause stems from insufficient null pointer validation in the Linux kernel's cryptographic scatterwalk API. When processing certain socket configurations, the kernel fails to properly validate memory references before dereferencing them, resulting in a null pointer dereference condition. The vulnerable code path does not adequately check for null pointers when walking through scatter-gather lists during cryptographic operations.

Attack Vector

The attack requires local access to the system with low-level user privileges. An attacker must:

1. Establish a socket with specific configuration parameters
2. Construct a malicious packet designed to trigger the vulnerable code path
3. Send the packet through the configured socket to trigger the null pointer dereference

The vulnerability manifests in the kernel's cryptographic scatterwalk functionality when processing specially crafted packets. Technical details can be found in the Linux Kernel Commit Update and Red Hat Bug Report #2219359.

Detection Methods for CVE-2023-6176

Indicators of Compromise

• Unexpected kernel panics or system crashes related to cryptographic operations
• Kernel oops messages referencing null pointer dereferences in crypto subsystem functions
• Suspicious socket activity involving cryptographic API calls from non-privileged users
• System logs showing scatterwalk-related kernel errors

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for null pointer dereference errors in cryptographic functions
• Implement auditd rules to track socket creation and cryptographic API usage by non-root users
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection and behavioral analysis
• Use kernel tracing tools (ftrace, eBPF) to monitor scatterwalk function calls for anomalous patterns

Monitoring Recommendations

• Enable kernel crash dump collection to capture forensic data in case of exploitation attempts
• Configure centralized logging to aggregate kernel error messages across all Linux systems
• Implement alerting for repeated kernel panics or crypto subsystem errors
• Monitor for privilege escalation attempts following any cryptographic API anomalies

How to Mitigate CVE-2023-6176

Immediate Actions Required

• Apply the latest kernel security updates from your Linux distribution
• Review and restrict local user access on critical systems
• Monitor systems for signs of exploitation attempts
• Consider applying kernel live patches where available (see Packet Storm Security Notice LSN-0100-1)

Patch Information

The vulnerability has been addressed in the upstream Linux kernel via commit cfaa80c91f6f99b9342b6557f0f0e1143e434066. Red Hat has released security advisories with patches for affected Enterprise Linux versions:

• RHSA-2024:2394 - Red Hat Enterprise Linux security update
• RHSA-2024:2950 - Red Hat Enterprise Linux security update
• RHSA-2024:3138 - Red Hat Enterprise Linux security update

For additional details, refer to the Red Hat CVE-2023-6176 Details page.

Workarounds

• Restrict local user access to minimize potential attack surface until patches can be applied
• Implement SELinux or AppArmor policies to limit cryptographic API access to essential services only
• Use kernel module parameters to restrict cryptographic functionality where not required
• Consider network segmentation to limit access to systems where immediate patching is not feasible

# Check current kernel version for vulnerability status
uname -r

# For Red Hat/CentOS systems, check for available security updates
yum check-update --security

# Apply kernel security updates (requires reboot)
yum update kernel --security

# Verify SELinux is enforcing to provide additional protection
getenforce