CVE-2021-28643 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 a Type Confusion vulnerability. An unauthenticated attacker could leverage this vulnerability to disclose sensitive memory 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 • 06/13/2026
This vulnerability represents a critical type confusion flaw affecting multiple versions of Adobe Acrobat Reader DC, specifically targeting the software's memory management mechanisms. The issue manifests as a type confusion vulnerability that allows attackers to manipulate object types during runtime execution, potentially leading to unauthorized memory access patterns. The vulnerability exists within the document parsing and rendering components of the application where type checking mechanisms fail to properly validate object classifications during processing operations. According to CWE-466, this falls under the category of "Use of Incorrectly Specified Index" and "Use of a Non-integer as an Index" which directly relates to improper type handling in memory operations.
The technical exploitation requires an unauthenticated attacker to craft a malicious file that triggers the type confusion during document processing, specifically when the application attempts to handle objects of unexpected types. This vulnerability operates at the memory management level where the application's type system fails to maintain proper object boundaries, allowing for potential information disclosure attacks. The attack vector requires user interaction since victims must open the malicious file for exploitation to occur, making this a client-side attack that relies on social engineering or phishing techniques to succeed.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the capability to extract sensitive memory contents that may contain credentials, personal data, or application-specific information. Attackers can potentially leverage this to gain insights into the application's internal state, memory layout, or even extract cryptographic keys and other sensitive materials. This vulnerability aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1557.001 for "Adversarial Process Discovery" as it enables attackers to gather system information and potentially escalate privileges through memory-based attacks.
Mitigation strategies should prioritize immediate patching of affected versions to address the root cause in the type validation mechanisms. Organizations must implement strict file validation policies and user education programs to prevent opening suspicious documents from untrusted sources. Network-based defenses such as email filtering and web proxies should be configured to block potentially malicious PDF files. Additionally, application sandboxing and privilege separation techniques can limit the potential damage from successful exploitation attempts. The vulnerability demonstrates the importance of proper type checking and memory safety practices as outlined in secure coding guidelines and standards such as those defined in the CERT Secure Coding Standards for C and C++ languages.