CVE-2021-21044 in Acrobat Reader
Summary
by MITRE • 02/12/2021
Acrobat Reader DC versions versions 2020.013.20074 (and earlier), 2020.001.30018 (and earlier) and 2017.011.30188 (and earlier) are affected by an Out-of-bounds Write vulnerability when parsing a crafted jpeg file. 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 • 02/28/2021
The vulnerability identified as CVE-2021-21044 represents a critical out-of-bounds write flaw within Adobe Acrobat Reader DC applications across multiple version ranges including 2020.013.20074 and earlier, 2020.001.30018 and earlier, and 2017.011.30188 and earlier. This vulnerability specifically manifests when the application processes a specially crafted jpeg file, indicating a memory corruption issue in the image parsing component. The flaw falls under the CWE-787 Out-of-bounds Write category, which is classified as a severe memory safety issue that can lead to arbitrary code execution. The vulnerability requires an unauthenticated attacker to deliver a malicious jpeg file to a victim, making it a remote code execution vector that relies on social engineering or phishing attacks to achieve compromise.
The technical implementation of this vulnerability occurs within the jpeg parsing functionality of Acrobat Reader DC, where insufficient bounds checking allows an attacker to write data beyond the allocated memory buffer. When a victim opens the malicious jpeg file, the application's image processing engine fails to properly validate the file structure, leading to memory corruption that can be exploited to overwrite critical memory locations. This type of vulnerability is particularly dangerous because it operates within the context of the current user, meaning successful exploitation could result in full system compromise without requiring elevated privileges. The exploitation requires user interaction as the victim must actively open the malicious file, but once opened, the malicious code can execute with the same permissions as the legitimate user.
The operational impact of CVE-2021-21044 extends beyond simple code execution to encompass potential full system compromise, data theft, and persistent backdoor installation. The vulnerability affects users who frequently handle pdf documents, particularly in enterprise environments where Acrobat Reader DC is commonly deployed. Organizations using these vulnerable versions face significant risk from targeted attacks, as the exploitation requires minimal user interaction beyond opening a malicious file, making it particularly effective in phishing campaigns. The vulnerability also impacts the broader security posture of affected systems, as successful exploitation can provide attackers with a foothold for further lateral movement within networks. This aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, where attackers can leverage the executed code to establish persistence and execute additional malicious activities.
Mitigation strategies for CVE-2021-21044 primarily focus on immediate patching of affected Adobe Acrobat Reader DC versions, with the most effective approach being the installation of the latest security updates from Adobe. Organizations should implement strict file validation policies, particularly for jpeg files that may be embedded within pdf documents, and consider deploying sandboxing solutions to isolate document processing activities. Network-based mitigations can include blocking suspicious file types at network perimeters and implementing email filtering solutions that identify and quarantine potentially malicious attachments. The vulnerability also underscores the importance of user security awareness training to prevent successful social engineering attacks that rely on users opening malicious files. Additionally, organizations should consider implementing application whitelisting policies to restrict the execution of untrusted applications and reduce the attack surface for exploitation attempts.