CVE-2021-28632 in Acrobat Reader
Summary
by MITRE • 08/25/2021
Acrobat Reader DC versions versions 2021.001.20155 (and earlier), 2020.001.30025 (and earlier) and 2017.011.30196 (and earlier) are affected by an Use After Free vulnerability. An unauthenticated attacker could leverage this vulnerability to achieve arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.
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Analysis
by VulDB Data Team • 08/29/2021
The vulnerability identified as CVE-2021-28632 represents a critical use after free flaw in Adobe Acrobat Reader DC across multiple version ranges including 2021.001.20155 and earlier, 2020.001.30025 and earlier, and 2017.011.30196 and earlier. This type of vulnerability occurs when a program continues to reference memory after it has been freed, creating a scenario where subsequent memory operations can corrupt or overwrite data structures that were previously allocated. The flaw manifests within the document parsing and rendering components of Acrobat Reader, specifically when processing maliciously crafted pdf files that trigger improper memory management during object deallocation.
The technical implementation of this vulnerability stems from inadequate memory management practices within the application's pdf parser. When a malicious pdf file is processed, the application allocates memory for various objects and structures during parsing operations. However, the memory deallocation process fails to properly invalidate pointers or maintain proper reference counts, allowing subsequent operations to access freed memory locations. This creates a window where an attacker can manipulate the memory layout to overwrite critical data structures or function pointers, ultimately enabling arbitrary code execution. The vulnerability operates under the common weakness enumeration CWE-416 which specifically addresses use after free conditions in software applications.
The operational impact of CVE-2021-28632 is significant as it enables remote code execution without authentication requirements, making it particularly dangerous in enterprise environments where users frequently open pdf documents from untrusted sources. The exploitation requires only user interaction through opening a malicious file, which can be delivered via email attachments, web downloads, or compromised websites. This attack vector aligns with the tactics described in the attack pattern taxonomy under ATT&CK framework's T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code on target systems. The privilege escalation aspect is limited to the context of the current user, but this still represents a serious security compromise given that many users operate with elevated privileges or have access to sensitive organizational data.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected Acrobat Reader versions to the latest security updates provided by Adobe. Organizations should implement comprehensive email filtering and web proxy solutions to prevent users from accessing potentially malicious pdf files. Security teams should also consider implementing application whitelisting policies that restrict execution of unauthorized pdf readers while maintaining necessary business functionality. Additionally, user education programs should emphasize the importance of not opening unexpected pdf attachments and verifying document sources before opening. The vulnerability demonstrates the critical importance of proper memory management practices in security-critical applications and highlights the need for regular security assessments and code reviews to identify similar use after free conditions that could lead to similar exploitation scenarios.