CVE-2021-44701 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 use-after-free vulnerability in the processing of Format event actions 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.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/19/2022
This vulnerability represents a critical use-after-free condition in Adobe Acrobat Reader DC affecting multiple versions including 21.007.20099 and earlier, 20.004.30017 and earlier, and 17.011.30204 and earlier. The flaw occurs during the processing of Format event actions within the PDF parsing mechanism, creating a scenario where freed memory locations can be accessed and potentially overwritten by malicious code. This type of vulnerability falls under the CWE-416 category, specifically addressing use-after-free conditions that represent one of the most dangerous classes of memory safety issues in software applications.
The technical exploitation of this vulnerability requires a sophisticated attack vector involving crafted PDF files containing malicious Format event actions that trigger the use-after-free condition. When a victim opens such a malicious document, the PDF parser processes the Format event action which leads to improper memory management, allowing an attacker to manipulate freed memory locations. The vulnerability specifically targets the memory management routines responsible for handling event actions in PDF documents, making it particularly dangerous as it operates within the legitimate document processing flow of the application.
The operational impact of this vulnerability extends beyond simple code execution, as it allows attackers to gain arbitrary code execution in the context of the current user account. This means that successful exploitation could result in complete system compromise, data exfiltration, or further lateral movement within a network environment. The requirement for user interaction through document opening creates a social engineering component that makes this vulnerability particularly concerning for enterprise environments where users frequently open PDF documents from various sources. The vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1203 for exploitation for client execution, representing a classic attack pattern for privilege escalation and system compromise.
Organizations should immediately implement mitigations including prompt patching of affected Adobe Acrobat Reader versions to address the underlying memory management issues. Additionally, implementing strict document handling policies that restrict PDF file execution from untrusted sources, deploying sandboxing solutions for PDF processing, and establishing user awareness training programs can significantly reduce the attack surface. Network-based protections such as web application firewalls and email filtering systems should be configured to block suspicious PDF content, while endpoint detection and response solutions can monitor for anomalous behavior indicative of exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date software patches and implementing defense-in-depth strategies to protect against sophisticated exploitation techniques that leverage memory corruption vulnerabilities.