CVE-2021-44740 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 flaw occurs during the parsing of specially crafted malicious files, where the application fails to properly validate pointer references before dereferencing them. This type of vulnerability falls under the CWE-476 category of null pointer dereference, which is a common class of software defects that can lead to application instability and potential system compromise. The vulnerability exists within the document parsing engine of Acrobat Reader, specifically when processing malformed or crafted input files that contain unexpected pointer values.
The operational impact of this vulnerability is significant as it enables an unauthenticated remote attacker to execute a denial-of-service attack against targeted systems. The attack requires user interaction since victims must voluntarily open the malicious file, making it a client-side exploitation vector that relies on social engineering or phishing techniques to succeed. When a user opens the crafted file, the application crashes or becomes unresponsive due to the null pointer dereference, effectively rendering the Acrobat Reader application unusable for that session. This disruption can be particularly problematic in enterprise environments where document processing is critical for business operations, potentially leading to productivity loss and requiring system administrator intervention to restore normal functionality.
From a cybersecurity perspective, this vulnerability aligns with the ATT&CK framework's technique T1203, which involves exploitation of known vulnerabilities in software applications. The attack vector represents a classic client-side exploitation scenario where the attacker crafts a malicious document designed to trigger the null pointer dereference during normal application operation. The vulnerability demonstrates poor input validation practices within the document parsing component of Acrobat Reader, where the application does not adequately sanitize or validate incoming file data before attempting to dereference pointers. The lack of proper error handling mechanisms means that when the application encounters unexpected null pointer values during file parsing, it fails catastrophically rather than gracefully handling the error condition. This behavior makes the vulnerability particularly attractive to threat actors seeking to disrupt user productivity or create cover for more sophisticated attacks.
The recommended mitigations include immediate deployment of security patches provided by Adobe to address the null pointer dereference vulnerability, as well as implementing user education programs to raise awareness about opening suspicious documents from unknown sources. Organizations should also consider implementing file validation mechanisms that can detect and quarantine potentially malicious documents before they reach end users. Network security controls such as email filtering and web proxies can help prevent users from accessing malicious files through common attack vectors. Additionally, system administrators should monitor for unusual application crashes or denial-of-service events that might indicate exploitation attempts, and maintain up-to-date incident response procedures to quickly address any successful exploitation attempts. The vulnerability serves as a reminder of the importance of robust input validation and error handling in software applications, particularly those that process untrusted data from external sources.