CVE-2021-28554 in Acrobat Reader
Summary
by MITRE • 08/25/2021
Acrobat Reader DC versions versions 2021.001.20155 (and earlier), 2020.001.30025 (and earlier) and 2017.011.30196 (and earlier) are affected by an Out-of-bounds Read 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 • 08/29/2021
The vulnerability identified as CVE-2021-28554 represents a critical out-of-bounds read flaw affecting multiple versions of Adobe Acrobat Reader DC, specifically targeting versions up to 2021.001.20155, 2020.001.30025, and 2017.011.30196. This type of vulnerability falls under the CWE-125 category of out-of-bounds read conditions, where an application attempts to access memory locations beyond the allocated buffer boundaries. The flaw manifests when the affected software processes maliciously crafted PDF files, creating a scenario where memory corruption can occur and potentially lead to arbitrary code execution. The vulnerability is particularly concerning because it operates without requiring authentication, making it accessible to attackers who can deliver malicious payloads through various vectors including email attachments, web downloads, or compromised websites.
The technical exploitation of this vulnerability requires user interaction, meaning that a victim must actively open a specially crafted malicious file for the attack to succeed. This user interaction requirement places the vulnerability in the context of social engineering campaigns where attackers must convince users to open suspicious documents. When a user opens the malicious PDF, the Acrobat Reader application attempts to parse the file structure in a manner that triggers the out-of-bounds read condition, potentially allowing an attacker to manipulate memory contents and execute arbitrary code within the security context of the currently logged-in user. The attack chain typically involves crafting a PDF file that contains malformed data structures which, when processed by the vulnerable application, cause memory access violations that can be leveraged for code execution.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on Acrobat Reader for document processing, as it can enable attackers to execute malicious code on target systems without requiring administrative privileges. The arbitrary code execution capability means that attackers could potentially install malware, steal sensitive information, or establish persistent access to compromised systems. The vulnerability's presence in widely deployed software versions makes it particularly attractive to threat actors conducting mass exploitation campaigns, as the attack surface is extensive across various organizational environments. The fact that this vulnerability affects multiple release lines spanning several years indicates that organizations may have been exposed to risk for extended periods without proper patch management.
The mitigation strategy for CVE-2021-28554 primarily involves immediate patching of affected Adobe Acrobat Reader DC installations to the latest available versions that contain fixes for the out-of-bounds read vulnerability. Organizations should implement comprehensive patch management procedures to ensure timely deployment of security updates across all systems. Additionally, network security controls such as email filtering, web proxies, and application whitelisting can provide additional defense-in-depth layers to prevent users from accessing potentially malicious PDF files. The vulnerability aligns with ATT&CK technique T1204.002 for valid accounts and T1059.001 for command and scripting interpreter, as exploitation typically involves legitimate user accounts and command execution within the compromised system context. Organizations should also consider implementing user awareness training to reduce the likelihood of successful social engineering attacks that rely on user interaction with malicious documents.