CVE-2021-44741 in Acrobat Reader
Summary
by MITRE • 01/14/2022
Acrobat Reader DC version 21.007.20099 (and earlier), 20.004.30017 (and earlier) and 17.011.30204 (and earlier) are affected by a Null pointer dereference vulnerability when parsing a specially crafted file. An unauthenticated attacker could leverage this vulnerability to achieve an application denial-of-service 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 • 01/19/2022
This vulnerability represents a critical null pointer dereference flaw in Adobe Acrobat Reader DC across multiple version ranges including 21.007.20099 and earlier, 20.004.30017 and earlier, and 17.011.30204 and earlier. The technical implementation involves the application's failure to properly validate pointer references during file parsing operations, specifically when processing specially crafted malicious files. This weakness falls under the CWE-476 category of NULL Pointer Dereference, which occurs when an application attempts to access a memory location through a pointer that has not been properly initialized to point to valid memory. The vulnerability manifests when the parsing routine encounters malformed input data that triggers an unexpected null pointer access, leading to application instability and potential crash conditions.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions as it creates a significant attack surface for malicious actors seeking to disrupt legitimate user activities. The requirement for user interaction makes this a particularly concerning threat vector since it relies on social engineering or phishing campaigns to deliver malicious files to unsuspecting victims. When a user opens a crafted file, the application crashes or becomes unresponsive, effectively preventing legitimate document access and potentially disrupting business operations. This vulnerability directly maps to ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code or cause system disruption.
The exploitation scenario requires an attacker to craft a malicious file that triggers the null pointer dereference condition during parsing operations, typically involving malformed PDF structures or embedded objects that cause the application to attempt accessing uninitialized memory locations. This type of vulnerability represents a classic software bug that can be exploited through file-based attacks, where the attacker needs to convince the user to open a malicious document. The vulnerability affects multiple version ranges, indicating a persistent flaw in the application's parsing logic that was not adequately addressed in the affected releases. Organizations using these versions face significant risk as the vulnerability can be leveraged in targeted attacks against specific users or broader campaigns where malicious documents are distributed through various channels including email attachments, malicious websites, or compromised software distribution points.
Mitigation strategies should focus on immediate patching of affected versions to address the root cause of the null pointer dereference. Adobe has released security updates that resolve this issue by implementing proper pointer validation and error handling during file parsing operations. Organizations should also implement user education programs to reduce the likelihood of successful social engineering attacks, establish file filtering mechanisms to block suspicious document types, and maintain robust incident response procedures to quickly address any exploitation attempts. Additional protective measures include deploying application whitelisting policies, implementing sandboxing techniques for document handling, and maintaining up-to-date antivirus signatures that can detect and block known malicious file variants. The vulnerability underscores the importance of regular security updates and proper input validation in preventing exploitation of memory corruption flaws that can lead to system instability and service disruption.