CVE-2023-52340: Linux Kernel IPv6 DoS Vulnerability

CVE-2023-52340 Overview

CVE-2023-52340 is a resource exhaustion vulnerability in the IPv6 implementation of the Linux kernel before version 6.3. The flaw exists in net/ipv6/route.c where a max_size threshold can be easily consumed by an attacker, leading to a denial of service condition. When exploited, the system generates "network is unreachable" errors, effectively disrupting IPv6 network connectivity. The vulnerability can be triggered by sending IPv6 packets in a loop via a raw socket.

Critical Impact

This vulnerability allows remote attackers to exhaust the IPv6 routing table cache, causing network connectivity failures and denial of service on affected Linux systems without requiring authentication.

Affected Products

• Linux Kernel versions prior to 6.3
• Systems with IPv6 networking enabled
• Network appliances and servers running vulnerable Linux kernel versions

Discovery Timeline

• 2024-07-05 - CVE CVE-2023-52340 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-52340

Vulnerability Analysis

This vulnerability resides in the Linux kernel's IPv6 routing implementation, specifically within net/ipv6/route.c. The core issue is a resource exhaustion flaw (CWE-400) in how the kernel manages the IPv6 routing cache. The max_size threshold, which is designed to limit the number of cached routes, can be rapidly exhausted through carefully crafted network traffic.

When an attacker sends a continuous stream of IPv6 packets through a raw socket, each packet can trigger the creation of new routing cache entries. The kernel fails to properly rate-limit or validate these entries before the threshold is reached. Once the max_size limit is consumed, the kernel cannot add new routes to the cache, resulting in "network is unreachable" errors for legitimate IPv6 traffic.

The attack can be executed remotely over the network without any authentication requirements, making it particularly dangerous for internet-facing systems. The impact is limited to availability—there is no compromise of confidentiality or integrity.

Root Cause

The root cause of this vulnerability is improper resource management in the IPv6 routing subsystem. The max_size threshold mechanism in net/ipv6/route.c lacks sufficient protection against rapid consumption. The kernel does not implement adequate rate limiting or garbage collection mechanisms to prevent malicious actors from filling the routing cache faster than legitimate entries can be purged.

The fix, implemented in kernel commit af6d10345ca76670c1b7c37799f0d5576ccef277, addresses this by improving how the routing cache handles resource exhaustion scenarios and implementing better bounds checking on cache entry creation.

Attack Vector

The vulnerability is exploited via the network layer using raw sockets. An attacker can craft a simple program that opens a raw socket and continuously sends IPv6 packets to the target system. Each packet potentially creates a new routing cache entry, and by sending packets at a high rate, the attacker can quickly exhaust the max_size threshold.

The attack does not require any special privileges on the target system, nor does it require user interaction. The attacker only needs network connectivity to the vulnerable system. Once the routing cache is exhausted, the target system will be unable to route IPv6 traffic, effectively causing a denial of service for all IPv6-dependent services and applications.

For technical details on the vulnerability mechanism and the specific fix, refer to the Linux Kernel Commit af6d103.

Detection Methods for CVE-2023-52340

Indicators of Compromise

• Sudden increase in "network is unreachable" errors for IPv6 traffic
• Unusual growth in the IPv6 routing cache size approaching or hitting the max_size limit
• High volume of IPv6 packets originating from a single source via raw sockets
• System logs showing IPv6 routing failures or cache exhaustion messages

Detection Strategies

• Monitor network traffic for anomalous patterns of IPv6 packets, particularly those sent via raw sockets
• Implement kernel-level auditing to track routing cache utilization and alert when approaching threshold limits
• Deploy network intrusion detection systems (IDS) configured to detect IPv6 flooding patterns
• Use SentinelOne Singularity Platform for real-time kernel-level monitoring and behavioral analysis of network-related anomalies

Monitoring Recommendations

• Configure syslog monitoring to capture and alert on IPv6 routing errors and "network is unreachable" messages
• Establish baseline metrics for IPv6 routing cache utilization and set up alerts for deviations
• Monitor raw socket usage on systems, particularly for processes sending high volumes of IPv6 traffic
• Implement network flow analysis to detect potential denial of service attack patterns targeting IPv6

How to Mitigate CVE-2023-52340

Immediate Actions Required

• Upgrade to Linux kernel version 6.3 or later which contains the fix for this vulnerability
• Apply vendor-specific patches from your Linux distribution (Debian, Red Hat, Ubuntu, etc.)
• Monitor systems for signs of exploitation while patches are being deployed
• Consider temporarily disabling IPv6 on non-critical systems if patching cannot be performed immediately

Patch Information

The vulnerability has been addressed in Linux kernel version 6.3 through commit af6d10345ca76670c1b7c37799f0d5576ccef277. This fix improves the handling of the routing cache max_size threshold to prevent resource exhaustion attacks.

For detailed patch information, refer to the Linux Kernel ChangeLog 6.3. Debian users should review the Debian LTS Announcement June 2024 for distribution-specific updates. NetApp customers should consult the NetApp Security Advisory ntap-20240816-0005 for guidance on affected products.

Workarounds

• Disable IPv6 on systems where it is not required by adding ipv6.disable=1 to kernel boot parameters
• Implement network-level filtering to rate-limit IPv6 traffic from untrusted sources
• Configure firewall rules to restrict raw socket usage to trusted applications and users
• Increase monitoring on systems that cannot be immediately patched to detect exploitation attempts

# Configuration example - Disable IPv6 via sysctl (temporary workaround)
# Add to /etc/sysctl.conf or /etc/sysctl.d/99-disable-ipv6.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1

# Apply changes without reboot
sysctl -p

# Alternative: Disable IPv6 at boot via kernel parameter
# Add to GRUB_CMDLINE_LINUX in /etc/default/grub:
# ipv6.disable=1
# Then run: update-grub