CVE-2021-40724 in Acrobat Reader
Summary
by MITRE • 10/15/2021
Acrobat Reader for Android versions 21.8.0 (and earlier) are affected by a Path traversal vulnerability. An unauthenticated attacker could leverage this vulnerability to achieve 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 • 10/22/2021
Adobe Acrobat Reader for Android versions 21.8.0 and earlier contain a critical path traversal vulnerability that allows unauthenticated remote attackers to execute arbitrary code with the privileges of the current user. This vulnerability resides in the file handling mechanisms of the application and represents a significant security risk due to its potential for remote code execution without authentication. The flaw enables attackers to manipulate file paths during file processing, potentially allowing them to access or modify files outside of the intended directory structure. This type of vulnerability is classified under CWE-22 Path Traversal and falls within the broader category of directory traversal attacks that have been consistently identified as high-risk security flaws across multiple platforms and applications.
The technical implementation of this vulnerability occurs when the Acrobat Reader application processes specially crafted files that contain malicious path manipulation sequences. Attackers can construct file paths that include directory traversal characters such as ../ or ..\ to navigate outside the intended application directory boundaries. When the application attempts to open these malicious files, the path traversal occurs during file resolution, potentially allowing access to sensitive system resources or the ability to write files to arbitrary locations on the device. The vulnerability specifically affects Android versions where the file parsing logic fails to properly validate or sanitize file paths before processing them, creating a direct pathway for exploitation through user interaction.
The operational impact of this vulnerability is severe as it enables attackers to achieve full arbitrary code execution on affected devices without requiring authentication or elevated privileges. The exploitation requires only user interaction through the opening of a malicious file, making it particularly dangerous in environments where users may encounter compromised documents through email attachments, file sharing platforms, or malicious websites. Once successfully exploited, the attacker can execute code with the same privileges as the Acrobat Reader application, potentially leading to data theft, device compromise, or further network infiltration. The vulnerability affects all users of the affected Android versions, creating a widespread risk across organizations and individual users who rely on Adobe Acrobat Reader for document viewing.
Organizations and users should immediately update to Adobe Acrobat Reader version 21.9.0 or later to address this vulnerability, as no working exploit is known to exist in the wild but the potential for exploitation remains high given the severity of the flaw. System administrators should implement network monitoring to detect suspicious file downloads or access patterns that might indicate exploitation attempts. The mitigation strategy should include comprehensive user education about the risks of opening unknown or untrusted documents, particularly those received via email or downloaded from unverified sources. Security controls should be implemented to restrict file access permissions and monitor file system modifications. This vulnerability aligns with ATT&CK technique T1059 Command and Scripting Interpreter, as the exploitation leads to code execution, and T1203 Exploitation for Client Execution, as it specifically targets client-side applications for remote code execution. Additionally, the vulnerability demonstrates characteristics of T1566 Impersonation, where attackers can potentially impersonate legitimate application behavior to execute malicious code within the application context.