CVE-2021-28640 in Acrobat Reader
Summary
by MITRE • 08/20/2021
Acrobat Reader DC versions 2021.005.20054 (and earlier), 2020.004.30005 (and earlier) and 2017.011.30197 (and earlier) are affected by an Use-after-free vulnerability. An authenticated 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 • 05/30/2026
This vulnerability represents a critical use-after-free condition in Adobe Acrobat Reader DC across multiple version ranges including 2021.005.20054 and earlier, 2020.004.30005 and earlier, and 2017.011.30197 and earlier. The flaw occurs when the application processes maliciously crafted PDF files, specifically during memory management operations where freed memory blocks are subsequently accessed by the application. This type of vulnerability falls under CWE-416 which defines the use of freed memory condition as a fundamental memory safety issue. The vulnerability is particularly dangerous because it requires only user interaction to exploit, making it highly practical for social engineering attacks where victims must simply open a malicious file to be compromised.
The technical implementation of this use-after-free vulnerability allows an authenticated attacker to manipulate the application's memory management system in such a way that freed memory locations are reused for malicious purposes. When the vulnerable application processes a crafted PDF file, it may attempt to access memory that has already been deallocated, leading to unpredictable behavior that can be exploited to execute arbitrary code. This particular flaw demonstrates how improper memory handling in PDF processing libraries can create opportunities for privilege escalation attacks. The vulnerability is classified under the ATT&CK framework as a code execution technique through malicious document manipulation, specifically leveraging the T1204.002 sub-technique involving legitimate user interaction with malicious content.
The operational impact of this vulnerability extends beyond simple code execution as it provides attackers with a means to establish persistent access within user environments. Since the exploit requires only a single user interaction through file opening, it can be effectively deployed through phishing campaigns, malicious email attachments, or compromised websites. The fact that the exploitation occurs in the context of the current user means that attackers can potentially access local files, network resources, and perform actions within the user's permission scope. This vulnerability is particularly concerning in enterprise environments where users frequently interact with PDF documents from external sources, creating numerous potential attack vectors for threat actors seeking to establish footholds within networks.
Mitigation strategies for this vulnerability should focus on immediate remediation through patch management, ensuring all affected versions of Adobe Acrobat Reader DC are updated to patched releases. Organizations should implement strict email filtering and sandboxing of PDF files to prevent automatic execution of potentially malicious documents. Network-based protections including web proxies and content filtering systems can help prevent access to known malicious PDF content. Additionally, user education regarding the risks of opening untrusted PDF files remains crucial, as this vulnerability specifically requires user interaction to be exploited. Security teams should also consider implementing application whitelisting policies that restrict PDF processing to trusted applications only, reducing the attack surface for this specific class of vulnerability.