CVE-2021-34424: Zoom Meetings Information Disclosure Flaw

CVE-2021-34424 Overview

A memory information disclosure vulnerability was discovered across the entire Zoom product ecosystem, affecting multiple client applications, SDKs, and on-premise components. This vulnerability, classified as an Out-of-Bounds Read (CWE-125), potentially allows for the exposure of process memory state, enabling attackers to gain insight into arbitrary areas of the product's memory.

Critical Impact

This vulnerability affects an extensive range of Zoom products across all major platforms (Android, iOS, Linux, macOS, and Windows), including client applications, meeting SDKs, VDI plugins, and on-premise infrastructure components. Successful exploitation could expose sensitive information stored in process memory.

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 Azure Virtual Desktop Plugins before version 5.8.4.21112
• Zoom VDI Citrix Plugins before version 5.8.4.21112
• Zoom VDI VMware Plugins before version 5.8.4.21112
• Zoom Meeting SDK (Android, iOS, macOS, Windows) before version 5.7.6.x
• Zoom Video SDK before version 1.1.2
• Zoom on-premise Meeting Connector before version 4.8.12.20211115
• Zoom Hybrid components before November 2021 releases

Discovery Timeline

• 2021-11-24 - CVE-2021-34424 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-34424

Vulnerability Analysis

This vulnerability stems from an Out-of-Bounds Read condition (CWE-125) present across the Zoom software ecosystem. The flaw allows reading memory beyond the intended boundaries of a buffer, potentially exposing sensitive information stored in adjacent memory regions.

The vulnerability is particularly concerning due to its network-exploitable nature without requiring user interaction or authentication. An attacker can potentially extract sensitive data from the application's memory space, which may include session tokens, encryption keys, or other confidential information processed by the Zoom client.

The broad scope of affected products—spanning desktop clients, mobile applications, browser extensions, VDI plugins, and server-side components—significantly increases the attack surface for organizations using Zoom infrastructure.

Root Cause

The root cause is an Out-of-Bounds Read vulnerability where the application fails to properly validate memory access boundaries before reading data. This allows memory reads beyond the allocated buffer size, potentially exposing adjacent memory contents that may contain sensitive information.

In memory-based information disclosure vulnerabilities like this, improper bounds checking during data processing operations can lead to leakage of:

• Internal application state
• Cryptographic material
• User credentials or session data
• Memory addresses useful for bypassing ASLR

Attack Vector

The vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker could craft malicious network packets or meeting data that triggers the out-of-bounds read condition in vulnerable Zoom components.

Given the nature of video conferencing applications, potential attack scenarios include:

• Malicious meeting participants sending crafted data to other attendees
• Man-in-the-middle attacks against unencrypted communications
• Exploitation of on-premise Zoom infrastructure components accessible on the network

The vulnerability mechanism involves improper validation of buffer boundaries during memory read operations. When processing certain data structures, the application may read beyond the allocated buffer size, returning memory contents from adjacent regions. This can be triggered through specially crafted input that causes the application to miscalculate buffer boundaries or skip validation checks entirely. For detailed technical analysis, refer to the Packet Storm Security Advisory.

Detection Methods for CVE-2021-34424

Indicators of Compromise

• Unusual memory access patterns or application crashes in Zoom client processes
• Abnormal network traffic patterns to/from Zoom infrastructure containing unexpected data payloads
• Evidence of repeated connection attempts or malformed meeting join requests
• Memory dump files or crash reports indicating out-of-bounds read exceptions

Detection Strategies

• Monitor Zoom application version numbers across endpoints and block vulnerable versions from connecting
• Implement network-level inspection for anomalous Zoom protocol traffic patterns
• Deploy endpoint detection rules to identify memory access violations in Zoom processes
• Review crash telemetry for patterns consistent with memory disclosure exploitation attempts

Monitoring Recommendations

• Enable verbose logging on Zoom client applications to capture connection and processing events
• Monitor on-premise Zoom infrastructure components for unusual memory utilization patterns
• Implement alerting for any Zoom components running versions older than the patched releases
• Track network connections to Zoom services for anomalous behavior or data exfiltration indicators

How to Mitigate CVE-2021-34424

Immediate Actions Required

• Upgrade all Zoom Client for Meetings installations to version 5.8.4 or later immediately
• Update Zoom Rooms and Controllers for Zoom Rooms to version 5.8.3 or later
• Patch all Zoom VDI plugins to version 5.8.4.21112 or later
• Update on-premise Zoom infrastructure components to the November 2021 releases
• Audit all Zoom SDK integrations and upgrade to patched versions (5.7.6 or later for Meeting SDKs)

Patch Information

Zoom has released patches addressing this vulnerability across all affected product lines. Organizations should refer to the Zoom Security Bulletin for the complete list of patched versions and download links.

Key patched versions include:

• Zoom Client for Meetings: 5.8.4
• Zoom Rooms: 5.8.3
• Zoom VDI Plugins: 5.8.4.21112
• On-premise Meeting Connector: 4.8.12.20211115

Workarounds

• Restrict network access to on-premise Zoom infrastructure to trusted networks only
• Implement network segmentation to isolate Zoom services from sensitive internal resources
• Consider temporarily disabling unused Zoom components until patching can be completed
• Use web-based Zoom access for sensitive meetings while client updates are deployed

# Verify Zoom client version on Windows (PowerShell)
Get-ItemProperty "HKCU:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*" | 
Where-Object { $_.DisplayName -like "*Zoom*" } | 
Select-Object DisplayName, DisplayVersion

# Check Zoom version on macOS
defaults read /Applications/zoom.us.app/Contents/Info CFBundleShortVersionString

# List Zoom processes and verify versions on Linux
dpkg -l | grep zoom