CVE-2021-35986 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 Type Confusion vulnerability. An unauthenticated attacker could leverage this vulnerability to read arbitrary system information 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 • 05/17/2026
The Type Confusion vulnerability present in Adobe Acrobat Reader DC versions 2021.005.20054 and earlier, 2020.004.30005 and earlier, and 2017.011.30197 and earlier represents a critical security flaw that stems from improper handling of data types during program execution. This vulnerability falls under the CWE-843 category, which specifically addresses Type Confusion issues where a program incorrectly handles objects of different types, leading to potential exploitation. The flaw manifests when the application processes malformed input data that causes the interpreter to confuse data types, potentially allowing an attacker to manipulate memory operations and access system resources that should otherwise be restricted. This type of vulnerability is particularly dangerous because it can be leveraged to execute arbitrary code or read system information without proper authentication.
The technical exploitation of this vulnerability requires an attacker to craft a malicious file that triggers the Type Confusion condition when opened by a victim. The attack vector necessitates user interaction since the victim must open the malicious document for the exploit to be successful, making this a classic social engineering target. When the vulnerable application processes the crafted file, the Type Confusion error allows an attacker to manipulate how the program interprets memory locations, potentially leading to information disclosure or privilege escalation. The vulnerability exists within the document parsing and rendering components of Acrobat Reader DC, where different data structures are not properly validated before type conversion operations occur. This flaw can be mapped to ATT&CK technique T1059.007 which covers PowerShell and Command Scripting, as the exploitation may involve manipulating system resources through command execution pathways.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable attackers to gain unauthorized access to sensitive system information and potentially establish persistent access to compromised systems. Attackers can leverage this vulnerability to read arbitrary system information, which may include user credentials, system configuration details, or other sensitive data that could be used for further exploitation. The fact that the vulnerability requires user interaction limits its scope compared to fully automated attacks, but it remains a significant threat in targeted campaigns where social engineering can be employed to convince victims to open malicious documents. Organizations using these vulnerable versions of Acrobat Reader DC face increased risk of data breaches and unauthorized system access, particularly in environments where users frequently open PDF documents from untrusted sources.
Mitigation strategies for this vulnerability should include immediate patching of all affected Acrobat Reader DC versions to the latest security updates provided by Adobe. System administrators should implement strict document handling policies that limit the opening of PDF files from untrusted sources and consider deploying sandboxing solutions to isolate PDF processing activities. Network-level defenses such as email filtering and web proxy configurations can help prevent the delivery of malicious PDF files to end users. Organizations should also conduct regular security awareness training to educate users about the risks of opening suspicious documents and the importance of verifying document sources before opening them. Additionally, implementing application whitelisting policies and monitoring for unusual file access patterns can help detect potential exploitation attempts. The vulnerability's classification as a Type Confusion issue makes it particularly important to ensure that all software components properly validate data types during processing, as this type of flaw can often be exploited in chained attacks that combine multiple vulnerabilities to achieve more significant system compromise.