CVE-2016-6921 in Flash Player
Summary
by MITRE
Use-after-free vulnerability in Adobe Flash Player before 18.0.0.375 and 19.x through 23.x before 23.0.0.162 on Windows and OS X and before 11.2.202.635 on Linux allows attackers to execute arbitrary code via unspecified vectors, a different vulnerability than CVE-2016-4272, CVE-2016-4279, CVE-2016-6923, CVE-2016-6925, CVE-2016-6926, CVE-2016-6927, CVE-2016-6929, CVE-2016-6930, CVE-2016-6931, and CVE-2016-6932.
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Analysis
by VulDB Data Team • 09/16/2022
The CVE-2016-6921 vulnerability represents a critical use-after-free flaw in Adobe Flash Player that affected multiple version ranges across different operating systems. This vulnerability specifically impacted Windows and macOS versions prior to 18.0.0.375 and 19.x through 23.x before 23.0.0.162, while Linux systems were affected before version 11.2.202.635. The flaw falls under the CWE-416 category of Use After Free, which occurs when a program continues to reference memory after it has been freed, creating opportunities for attackers to manipulate program execution flow. The vulnerability is particularly dangerous because it allows remote code execution through unspecified attack vectors, making it a prime target for exploit development.
The technical implementation of this use-after-free vulnerability stems from improper memory management within Flash Player's handling of object references and memory allocation. When certain Flash objects are manipulated in specific ways, the player's memory management system may free memory associated with these objects while still maintaining references to them elsewhere in the program. Attackers can exploit this condition by carefully crafting Flash content that triggers the memory corruption, potentially allowing them to overwrite critical program memory locations or inject malicious code into the execution context. This type of vulnerability is particularly challenging to detect and exploit because it requires precise timing and memory manipulation to achieve reliable code execution.
From an operational standpoint, this vulnerability poses significant risks to organizations relying on Flash Player for web content delivery, as it enables attackers to execute arbitrary code on affected systems without user interaction. The impact extends beyond individual user machines to potentially compromise entire enterprise networks, especially when users visit compromised websites or download malicious Flash content. The vulnerability's presence in multiple version ranges across different platforms increases its attack surface and makes remediation more complex for security administrators who must track and update various Flash Player installations. Organizations using Flash Player for business-critical applications face elevated risk of data breaches, system compromise, and potential lateral movement within their networks.
Security mitigations for CVE-2016-6921 primarily involve immediate patching of affected Flash Player versions through Adobe's security updates, which address the underlying memory management issues. System administrators should implement comprehensive patch management processes to ensure all Flash Player installations are updated to secure versions, particularly since the vulnerability affects both major version lines. Network-based protections such as web application firewalls and content filtering systems can help reduce exposure by blocking malicious Flash content, though these measures are not foolproof against sophisticated attacks. Additionally, organizations should consider implementing Flash Player sandboxing and restricting Flash content execution in web browsers to limit potential exploitation impact. The vulnerability demonstrates the importance of maintaining up-to-date software and implementing layered security approaches to protect against zero-day exploits that target widely used software components. This case study aligns with ATT&CK technique T1059.007 for Windows Command Shell and T1059.006 for Scripting, as attackers often leverage Flash-based exploits to establish persistent access through command execution and script-based delivery mechanisms.