CVE-2020-14305: Linux Kernel VoIP H.323 DOS Vulnerability

CVE-2020-14305 Overview

An out-of-bounds memory write vulnerability exists in the Linux kernel's Voice Over IP H.323 connection tracking functionality. The flaw occurs when handling connections on IPv6 port 1720, allowing an unauthenticated remote attacker to corrupt kernel memory. This vulnerability can be exploited to crash the system, resulting in a denial of service condition. The highest threat from this vulnerability impacts confidentiality, integrity, and system availability.

Critical Impact

Unauthenticated remote attackers can exploit this out-of-bounds write flaw to crash affected Linux systems or potentially achieve arbitrary code execution, threatening the confidentiality, integrity, and availability of the system.

Affected Products

• Linux Linux Kernel (versions prior to 4.12)
• NetApp Cloud Backup
• NetApp A250 Firmware
• NetApp FAS 500f Firmware
• NetApp AFF 500f Firmware
• NetApp SolidFire Baseboard Management Controller Firmware

Discovery Timeline

• December 2, 2020 - CVE-2020-14305 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-14305

Vulnerability Analysis

The vulnerability resides in the Linux kernel's netfilter connection tracking module for H.323 VoIP protocol handling. The H.323 connection tracking helper (nf_conntrack_h323) is responsible for tracking and managing H.323 session states, including call signaling on port 1720. When processing IPv6 traffic on this port, the kernel fails to properly validate buffer boundaries before performing memory write operations.

The out-of-bounds write condition (CWE-787) can be triggered by sending specially crafted network packets to an affected system listening on IPv6 port 1720. Since the vulnerability does not require authentication, any network-accessible attacker can potentially exploit this flaw. Successful exploitation can lead to kernel memory corruption, system crashes, or potentially arbitrary code execution in the kernel context.

Root Cause

The root cause lies in improper boundary checking within the H.323 connection tracking code when handling IPv6 addresses. The kernel module fails to validate the size of incoming data against the allocated buffer space before writing, leading to memory corruption when processing oversized or malformed H.323 signaling messages over IPv6.

Attack Vector

The attack can be performed remotely over the network without requiring any user interaction or authentication. An attacker needs to send malicious H.323 protocol packets to port 1720 (the standard H.323 call signaling port) on an IPv6-enabled system with the nf_conntrack_h323 module loaded. The attack complexity is considered high as specific conditions must be met, including:

• The target system must have IPv6 enabled
• The nf_conntrack_h323 kernel module must be loaded
• Network connectivity to port 1720 must be available

While no public proof-of-concept exploits are currently available, the nature of the vulnerability as a remotely-triggerable kernel memory corruption issue makes it a significant security concern. Detailed technical information can be found in the OpenVZ Bug Report OVZ-7188 and the Netfilter Patch Submission.

Detection Methods for CVE-2020-14305

Indicators of Compromise

• Unexpected kernel panics or system crashes, particularly when H.323 VoIP traffic is present
• Kernel log messages indicating memory corruption or invalid memory access in nf_conntrack_h323 module
• Abnormal network traffic patterns targeting IPv6 port 1720
• System instability correlating with incoming H.323 signaling attempts

Detection Strategies

• Monitor kernel logs for oops or panic messages referencing the nf_conntrack_h323 module or netfilter subsystem
• Implement network intrusion detection rules to identify malformed H.323 packets targeting port 1720 over IPv6
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection and behavioral analysis
• Audit loaded kernel modules using lsmod to identify systems with nf_conntrack_h323 enabled

Monitoring Recommendations

• Enable detailed kernel logging to capture early warning signs of exploitation attempts
• Configure network monitoring to alert on unusual H.323 traffic volume or characteristics, especially over IPv6
• Implement SentinelOne's endpoint detection capabilities to monitor for kernel-level anomalies and memory corruption indicators
• Set up automated alerting for system stability issues that may indicate exploitation attempts

How to Mitigate CVE-2020-14305

Immediate Actions Required

• Update the Linux kernel to version 4.12 or later where the vulnerability has been patched
• If patching is not immediately possible, disable the nf_conntrack_h323 module if H.323 connection tracking is not required
• Block or restrict access to port 1720 over IPv6 at the network firewall level
• Review and apply vendor-specific patches from NetApp for affected storage and BMC firmware

Patch Information

The vulnerability has been addressed in Linux kernel version 4.12 and later. Administrators should apply the latest kernel updates available from their Linux distribution. Additional vendor-specific patches are available:

• Red Hat Bugzilla ID 1850716 - Red Hat security tracking
• NetApp Security Advisory ntap-20201210-0004 - NetApp product patches

For the original kernel patch, refer to the Netfilter Patch Submission.

Workarounds

• Disable the H.323 connection tracking module if not required: modprobe -r nf_conntrack_h323
• Add the module to the blacklist to prevent automatic loading
• Implement firewall rules to block inbound IPv6 traffic to port 1720 from untrusted sources
• Consider disabling IPv6 if not required for business operations

# Disable and blacklist nf_conntrack_h323 module
modprobe -r nf_conntrack_h323
echo "blacklist nf_conntrack_h323" >> /etc/modprobe.d/blacklist.conf

# Block IPv6 traffic to port 1720 using ip6tables
ip6tables -A INPUT -p tcp --dport 1720 -j DROP
ip6tables -A INPUT -p udp --dport 1720 -j DROP