CVE-2021-44707 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 an out-of-bounds write vulnerability that could result in 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 • 01/19/2022
This vulnerability exists in Adobe Acrobat Reader DC versions 21.007.20099 and earlier, 20.004.30017 and earlier, and 17.011.30204 and earlier, representing a critical out-of-bounds write flaw that can lead to arbitrary code execution. The vulnerability stems from insufficient input validation within the application's handling of specially crafted files, specifically affecting the parsing of certain document structures. The flaw allows an attacker to manipulate memory allocation patterns during file processing, creating conditions where data can be written beyond the boundaries of allocated memory buffers. This type of vulnerability falls under CWE-787, which specifically addresses out-of-bounds write conditions in software applications. The attack requires user interaction through social engineering tactics where victims must open a maliciously crafted file, making this a typical client-side exploitation vector that aligns with ATT&CK technique T1203 for legitimate program exploitation.
The technical implementation of this vulnerability occurs when the Acrobat Reader processes malformed document elements that trigger improper memory management during parsing operations. When the application encounters unexpected data structures within PDF files, it fails to properly validate buffer sizes before writing data, resulting in memory corruption that can be leveraged by attackers to execute arbitrary code with the privileges of the current user. The out-of-bounds write condition typically manifests during the rendering or parsing of complex PDF elements such as embedded objects, graphics, or metadata sections that contain malformed data sequences. This vulnerability represents a classic memory safety issue where the application's memory management routines do not adequately check array bounds or buffer limits before performing write operations, creating opportunities for attackers to overwrite adjacent memory locations with malicious payloads.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a potential foothold for more sophisticated attacks within the victim's environment. Since the exploitation requires user interaction through opening malicious files, it typically follows phishing campaigns or malicious document distribution methods that leverage social engineering to convince victims to execute the payload. The privilege escalation potential is limited to the current user context, but this still represents a significant security risk as attackers can potentially access user files, credentials, or system resources available to that user account. The vulnerability's exploitation pathway aligns with ATT&CK tactic T1059 for command and scripting interpreter usage and T1068 for exploit for privilege escalation, making it a versatile threat vector in modern attack chains. Organizations using these affected versions of Acrobat Reader face substantial risk as the vulnerability can be exploited through various attack vectors including email attachments, web downloads, or malicious websites.
Mitigation strategies should prioritize immediate patching of affected software versions to address the root cause of the memory safety issue. Adobe has released security updates for all affected versions, and organizations should implement these patches through their standard software update procedures to prevent exploitation. Additional protective measures include implementing strict file validation policies that scan and quarantine suspicious PDF files before user access, utilizing sandboxing technologies to isolate document processing, and employing email filtering systems that can detect and block malicious attachments. Network-based defenses such as web application firewalls and content filtering solutions can help prevent users from accessing malicious documents through web interfaces. Security awareness training programs should emphasize the dangers of opening unexpected PDF files and educate users on recognizing potential social engineering attempts. Organizations should also consider implementing privileged access controls and monitoring for unusual file access patterns that might indicate exploitation attempts, as the vulnerability requires user interaction to be successful.