CVE-2021-34423: Zoom Meetings Buffer Overflow Vulnerability

CVE-2021-34423 Overview

A critical buffer overflow vulnerability (CWE-120) was discovered in the Zoom Client for Meetings affecting multiple platforms including Android, iOS, Linux, macOS, and Windows. This vulnerability exists in numerous Zoom products including the standard Meetings client, VDI plugins, Meeting SDKs, Video SDKs, and various on-premise connectors. The flaw allows a remote attacker to potentially crash the service or application, and more critically, could be leveraged to execute arbitrary code on affected systems.

Critical Impact

This buffer overflow vulnerability can be exploited remotely without authentication to crash Zoom services or execute arbitrary code across all major desktop and mobile platforms, affecting millions of enterprise and consumer users worldwide.

Affected Products

• Zoom Client for Meetings (Android, iOS, Linux, macOS, Windows) before version 5.8.4
• Zoom Client for Meetings for Blackberry (Android, iOS) before version 5.8.1
• Zoom Client for Meetings for Intune (Android, iOS) before version 5.8.4
• Zoom Client for Meetings for Chrome OS before version 5.0.1
• Zoom Rooms for Conference Room (Android, AndroidBali, macOS, Windows) before version 5.8.3
• Controllers for Zoom Rooms (Android, iOS, Windows) before version 5.8.3
• Zoom VDI Windows Meeting Client before version 5.8.4
• Zoom VDI Plugins (Azure Virtual Desktop, Citrix, VMware) before version 5.8.4.21112
• Zoom Meeting SDK (Android, iOS, macOS, Windows) before version 5.7.6.x
• Zoom Video SDK (Android, iOS, macOS, Windows) before version 1.1.2
• Zoom On-Premise Meeting Connector Controller/MMR before version 4.8.12.20211115
• Zoom On-Premise Recording Connector before version 5.1.0.65.20211116
• Zoom On-Premise Virtual Room Connector before version 4.4.7266.20211117
• Zoom Hybrid Zproxy before version 1.0.1058.20211116
• Zoom Hybrid MMR before version 4.6.20211116.131_x86-64

Discovery Timeline

• 2021-11-24 - CVE-2021-34423 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-34423

Vulnerability Analysis

This buffer overflow vulnerability resides in Zoom's chat message processing functionality. The flaw occurs when the application fails to properly validate the size of input data before copying it into a fixed-size memory buffer. When a specially crafted message exceeds the expected buffer boundaries, it can overwrite adjacent memory locations.

The vulnerability can be exploited remotely over the network without requiring any authentication or user interaction, making it particularly dangerous in enterprise environments where Zoom is ubiquitous for video conferencing. Successful exploitation could allow an attacker to execute arbitrary code with the privileges of the Zoom application, potentially leading to complete system compromise.

Root Cause

The root cause is a classic buffer overflow condition (CWE-120: Buffer Copy without Checking Size of Input) in the chat message processing component. The vulnerable code path fails to implement proper bounds checking when handling incoming message data, allowing memory corruption when oversized input is processed.

Attack Vector

The attack can be initiated remotely over the network. An attacker can exploit this vulnerability by sending specially crafted data to a vulnerable Zoom client or server component. According to technical references, the vulnerability specifically affects chat message processing, where malformed messages can trigger the buffer overflow condition.

The exploitation does not require authentication, and in many scenarios, the victim may not need to take any specific action beyond being connected to a meeting or having the Zoom client running. This network-based attack vector significantly increases the risk surface given Zoom's widespread deployment in corporate environments.

For detailed technical information about this vulnerability, refer to the Packet Storm Security advisory which documents the chat message processing buffer overflow mechanics.

Detection Methods for CVE-2021-34423

Indicators of Compromise

• Unexpected Zoom application crashes or service terminations, particularly during or after receiving chat messages
• Anomalous network traffic patterns to/from Zoom processes containing unusually large message payloads
• Memory access violations or segmentation faults in Zoom process logs
• Unusual child processes spawned by Zoom client applications

Detection Strategies

• Monitor Zoom application logs for abnormal crash patterns and memory-related errors
• Implement network monitoring to detect malformed or oversized chat message packets targeting Zoom infrastructure
• Deploy endpoint detection solutions to identify buffer overflow exploitation attempts and suspicious memory manipulation
• Use SentinelOne Singularity to detect and prevent exploitation of memory corruption vulnerabilities in real-time

Monitoring Recommendations

• Enable verbose logging on Zoom On-Premise infrastructure components to capture potential exploitation attempts
• Implement network intrusion detection signatures for known buffer overflow attack patterns targeting video conferencing applications
• Monitor system event logs for signs of code execution following Zoom process crashes
• Track Zoom client version deployment across the enterprise to identify vulnerable installations

How to Mitigate CVE-2021-34423

Immediate Actions Required

• Update all Zoom Client for Meetings installations to version 5.8.4 or later immediately
• Update Zoom Rooms for Conference Room to version 5.8.3 or later
• Upgrade all VDI plugins (Azure Virtual Desktop, Citrix, VMware) to version 5.8.4.21112 or later
• Update Zoom Meeting SDK components to version 5.7.6.x or later
• Patch all On-Premise connectors to the versions specified in the Zoom security bulletin

Patch Information

Zoom has released security patches addressing this vulnerability across all affected product lines. Organizations should consult the Zoom Security Bulletin for the complete list of patched versions and download links. The patches implement proper bounds checking to prevent buffer overflow conditions during message processing.

Workarounds

• Restrict Zoom network traffic through firewall rules to minimize external attack exposure until patches can be applied
• Disable chat functionality in Zoom meetings where possible through administrative policies
• Implement network segmentation to isolate Zoom infrastructure from critical systems
• Deploy endpoint protection with memory exploitation prevention capabilities to detect and block buffer overflow attacks

# Check installed Zoom version on Linux
zoom --version

# Check Zoom version on macOS
/Applications/zoom.us.app/Contents/MacOS/zoom --version

# On Windows, verify version via registry
reg query "HKEY_CURRENT_USER\Software\Zoom\Zoom" /v Version