CVE-2023-0394: Linux Kernel DOS Vulnerability

CVE-2023-0394 Overview

A NULL pointer dereference vulnerability has been identified in the Linux kernel's IPv6 networking subsystem. The flaw exists in the rawv6_push_pending_frames function located in net/ipv6/raw.c, which is responsible for handling raw IPv6 socket operations. When triggered, this vulnerability causes the system to crash, resulting in a denial of service condition.

This vulnerability affects the network subcomponent of the Linux kernel and can be exploited by a local attacker with low privileges. The flaw stems from improper pointer validation before dereferencing, allowing an attacker to trigger a kernel panic by manipulating raw IPv6 socket operations.

Critical Impact

Local attackers can crash the system by exploiting improper pointer handling in the IPv6 raw socket implementation, causing complete denial of service.

Affected Products

• Linux Kernel versions prior to the security patch
• Linux Kernel 6.2-rc1
• Linux Kernel 6.2-rc2
• Linux Kernel 6.2-rc3

Discovery Timeline

• 2023-01-26 - CVE-2023-0394 published to NVD
• 2025-03-31 - Last updated in NVD database

Technical Details for CVE-2023-0394

Vulnerability Analysis

The vulnerability resides in the rawv6_push_pending_frames function within the Linux kernel's IPv6 raw socket implementation. This function is called during the process of sending pending frames on a raw IPv6 socket. The flaw occurs due to inadequate validation of pointer values before they are dereferenced, specifically when processing IPv6 raw socket data structures.

When a local user with appropriate privileges creates and manipulates raw IPv6 sockets in a specific manner, the kernel may attempt to dereference a NULL pointer within this function. This results in a kernel panic, immediately crashing the system and causing a complete denial of service. The attack requires local access and low privileges to execute, making it a concern for multi-user systems and shared hosting environments.

The vulnerability is classified as CWE-476 (NULL Pointer Dereference), which occurs when the application dereferences a pointer that it expects to be valid but is actually NULL. In kernel context, such dereferencing triggers a kernel oops or panic, bringing down the entire system.

Root Cause

The root cause of this vulnerability is the absence of proper NULL pointer validation in the rawv6_push_pending_frames function before dereferencing critical data structures. The function fails to verify that the pointer to the pending frames structure is valid before attempting to access its members, leading to a NULL pointer dereference when the pointer is unexpectedly NULL.

This type of flaw typically occurs when:

• Error handling paths do not properly initialize or validate pointers
• Race conditions cause data structures to be freed while still in use
• Edge cases in socket state management are not properly handled

Attack Vector

The attack vector is local, requiring an attacker to have authenticated access to the target system. The attacker must be able to create raw IPv6 sockets and perform specific socket operations to trigger the vulnerable code path. While the attack requires low privileges, it does not require user interaction to execute.

The exploitation scenario involves:

1. Creating a raw IPv6 socket with specific configuration
2. Manipulating socket options or sending data in a manner that leads to a NULL pointer condition
3. Triggering the rawv6_push_pending_frames function to dereference the NULL pointer
4. Causing a kernel panic that crashes the entire system

The vulnerability mechanism involves improper pointer handling in the kernel's IPv6 raw socket processing. When rawv6_push_pending_frames is invoked under certain conditions, it attempts to access a pointer that should reference valid frame data but is instead NULL. The kernel's attempt to read from or write to memory address 0 triggers an immediate kernel panic. For detailed technical analysis, refer to the Linux Kernel Commit.

Detection Methods for CVE-2023-0394

Indicators of Compromise

• Unexpected system crashes or kernel panics with traces pointing to rawv6_push_pending_frames or net/ipv6/raw.c
• Kernel oops messages in system logs referencing NULL pointer dereference in IPv6 networking code
• Repeated system reboots without explanation on systems with IPv6 enabled
• Evidence of raw IPv6 socket creation by non-privileged users

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for NULL pointer dereference errors in the IPv6 networking stack
• Implement audit rules to track raw socket creation using auditd with rules targeting socket() syscalls for AF_INET6 with SOCK_RAW
• Deploy kernel-level monitoring tools to detect abnormal raw socket activity patterns
• Use SentinelOne's Singularity Platform for real-time kernel behavior monitoring and anomaly detection

Monitoring Recommendations

• Enable kernel crash dump collection to capture diagnostic information during system crashes
• Configure watchdog timers to automatically recover from kernel panics and log the events
• Monitor for unusual patterns in IPv6 raw socket usage across the environment
• Implement centralized log aggregation to correlate kernel crash events across multiple systems

How to Mitigate CVE-2023-0394

Immediate Actions Required

• Update the Linux kernel to a patched version that includes commit cb3e9864cdbe35ff6378966660edbcbac955fe17
• Review and apply available distribution-specific security updates from Debian, Red Hat, and other vendors
• Restrict raw socket capabilities using Linux capabilities to limit which users can create raw sockets
• Consider temporarily disabling IPv6 on systems where it is not required until patching is complete

Patch Information

The vulnerability has been addressed in the official Linux kernel through commit cb3e9864cdbe35ff6378966660edbcbac955fe17. This commit adds proper NULL pointer validation before dereferencing in the rawv6_push_pending_frames function.

Patches are available from:

• Linux Kernel Commit
• Debian LTS Announcement March 2023
• Debian LTS Announcement May 2023
• NetApp Security Advisory NTAP-20230302-0005

Workarounds

• Restrict access to raw sockets by removing CAP_NET_RAW capability from untrusted users and processes
• Use network namespaces to isolate potentially vulnerable workloads
• Disable IPv6 entirely if not required for operations using kernel boot parameters
• Implement strict access controls to limit local user access to affected systems

# Restrict raw socket capability for specific users/processes
# Remove CAP_NET_RAW from a binary
setcap -r /path/to/binary

# Disable IPv6 via sysctl (temporary workaround)
sysctl -w net.ipv6.conf.all.disable_ipv6=1
sysctl -w net.ipv6.conf.default.disable_ipv6=1

# Make sysctl changes persistent
echo "net.ipv6.conf.all.disable_ipv6 = 1" >> /etc/sysctl.conf
echo "net.ipv6.conf.default.disable_ipv6 = 1" >> /etc/sysctl.conf