CVE-2020-9633: Adobe Flash Player Use-After-Free Flaw

CVE-2020-9633 Overview

CVE-2020-9633 is a use after free vulnerability affecting Adobe Flash Player across multiple platforms and browser integrations. This memory corruption flaw exists in Adobe Flash Player Desktop Runtime 32.0.0.371 and earlier versions, as well as Adobe Flash Player for Google Chrome 32.0.0.371 and earlier, and Adobe Flash Player for Microsoft Edge and Internet Explorer 32.0.0.330 and earlier. Successful exploitation of this vulnerability could allow an attacker to achieve arbitrary code execution in the context of the current user.

Critical Impact

This use after free vulnerability enables remote attackers to execute arbitrary code on affected systems without authentication, potentially leading to complete system compromise across Windows, macOS, Linux, and Chrome OS platforms.

Affected Products

• Adobe Flash Player Desktop Runtime versions 32.0.0.371 and earlier (Windows, macOS, Linux)
• Adobe Flash Player for Google Chrome versions 32.0.0.371 and earlier (Windows, macOS, Linux, Chrome OS)
• Adobe Flash Player for Microsoft Edge and Internet Explorer versions 32.0.0.330 and earlier (Windows 10, Windows 8.1)

Discovery Timeline

• 2020-06-12 - CVE-2020-9633 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-9633

Vulnerability Analysis

CVE-2020-9633 is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Adobe Flash Player, this vulnerability allows attackers to craft malicious Flash content that triggers the use after free condition, potentially corrupting memory in a way that leads to arbitrary code execution.

The network-based attack vector means that exploitation can occur remotely, typically through malicious websites hosting crafted SWF files or through malicious advertisements (malvertising). No authentication is required, and no user interaction beyond visiting a compromised page is necessary for exploitation.

Root Cause

The vulnerability stems from improper memory management within Adobe Flash Player's runtime engine. When certain objects are deallocated, the application fails to properly invalidate references to the freed memory. Subsequent operations that attempt to access these dangling pointers can lead to memory corruption, which attackers can leverage to redirect program execution flow.

Use after free vulnerabilities in browser plugins like Flash Player are particularly dangerous because they can be triggered simply by rendering malicious content, making drive-by download attacks feasible.

Attack Vector

The attack vector for CVE-2020-9633 is network-based exploitation through malicious Flash content:

1. An attacker crafts a malicious SWF file designed to trigger the use after free condition
2. The victim visits a web page containing the malicious Flash content, either directly or through an embedded iframe
3. When Flash Player processes the content, specific operations trigger object deallocation while references remain active
4. Subsequent access to the freed memory allows the attacker to control execution flow
5. The attacker achieves arbitrary code execution in the context of the user's browser process

Due to the nature of browser-based exploitation, this vulnerability could be leveraged in targeted attacks or large-scale campaigns through compromised advertising networks.

Detection Methods for CVE-2020-9633

Indicators of Compromise

• Presence of suspicious SWF files in browser cache or temporary directories
• Unexpected Flash Player process crashes or error logs indicating memory corruption
• Network connections to known malicious domains hosting Flash-based exploits
• Unusual child processes spawned from browser or Flash Player processes

Detection Strategies

• Monitor for attempts to load Flash content from untrusted or newly-registered domains
• Implement network-based detection for known Flash exploit signatures and shellcode patterns
• Use endpoint detection to identify anomalous behavior from Flash Player processes
• Deploy application control policies to restrict Flash Player execution to trusted content only

Monitoring Recommendations

• Enable enhanced logging for browser plugin activities and Flash Player events
• Configure SIEM rules to detect patterns associated with Flash-based exploitation attempts
• Monitor process creation events for suspicious child processes of browser applications
• Track network connections originating from Flash Player to identify potential C2 communication

How to Mitigate CVE-2020-9633

Immediate Actions Required

• Update Adobe Flash Player to the latest version immediately via Adobe Flash Player Security Advisory
• Consider disabling or uninstalling Adobe Flash Player entirely, as it reached end-of-life in December 2020
• Configure browsers to block Flash content by default or require click-to-play activation
• Implement network filtering to block known Flash exploit delivery domains

Patch Information

Adobe has released a security update addressing this vulnerability as documented in Adobe Security Bulletin APSB20-30. Organizations should update to Adobe Flash Player version 32.0.0.387 or later. However, given that Adobe Flash Player reached end-of-life on December 31, 2020, the recommended approach is to completely remove Flash Player from all systems.

Linux distributions such as Gentoo have also released advisories, as noted in Gentoo GLSA 202006-09, providing guidance for affected users.

Workarounds

• Disable Adobe Flash Player in browser settings or via group policy
• Use browser extensions that block Flash content by default
• Implement application whitelisting to prevent unauthorized Flash content execution
• Configure network security appliances to inspect and block malicious SWF files

# Configuration example - Disable Flash Player via Windows Registry (Group Policy)
# Create registry key to disable Flash in Internet Explorer
reg add "HKLM\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{D27CDB6E-AE6D-11CF-96B8-444553540000}" /v "Compatibility Flags" /t REG_DWORD /d 1024 /f

# For Chrome, Flash can be disabled via enterprise policy
# Create policy file at: /etc/opt/chrome/policies/managed/flash_policy.json
# {"DefaultPluginsSetting": 2, "PluginsBlockedForUrls": ["*"]}