CVE-2021-28637 in Acrobat Reader
Summary
by MITRE • 08/20/2021
Acrobat Reader DC versions 2021.005.20054 (and earlier), 2020.004.30005 (and earlier) and 2017.011.30197 (and earlier) are affected by an out-of-bounds read vulnerability. An unauthenticated attacker could leverage this vulnerability achieve arbitrary read / write system information 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 • 08/20/2021
This vulnerability represents a critical out-of-bounds read flaw in Adobe Acrobat Reader DC across multiple version ranges including 2021.005.20054 and earlier, 2020.004.30005 and earlier, and 2017.011.30197 and earlier. The vulnerability stems from insufficient bounds checking within the application's file processing routines when handling specially crafted PDF documents. This flaw allows an unauthenticated remote attacker to execute arbitrary read and write operations against system memory in the context of the currently logged-in user. The technical implementation involves the application failing to properly validate array indices or buffer boundaries when parsing maliciously constructed PDF elements, leading to memory access violations that can be exploited for data extraction or modification.
The operational impact of this vulnerability extends beyond simple information disclosure as it creates potential pathways for privilege escalation and system compromise. Attackers can leverage this issue through social engineering campaigns where victims open malicious PDF files, making it particularly dangerous in targeted attacks against organizations. The vulnerability aligns with CWE-129 weakness category which addresses insufficient validation of length of input buffers, specifically manifesting as improper bounds checking during file parsing operations. This flaw can be mapped to ATT&CK technique T1059.007 for command and scripting interpreter, where the arbitrary read/write capabilities may enable attackers to manipulate system resources or extract sensitive information from memory.
Security professionals should recognize this vulnerability as a prime candidate for exploitation in advanced persistent threat campaigns due to Acrobat Reader's widespread deployment across enterprise environments. The requirement for user interaction through file opening creates a realistic attack vector that can be amplified through phishing campaigns or malicious website downloads. Organizations must prioritize immediate patching of affected versions while implementing additional controls such as PDF file scanning, restricted user permissions, and network-based intrusion detection systems monitoring for suspicious PDF processing activities. The vulnerability demonstrates the critical importance of maintaining updated software versions and implementing defense-in-depth strategies to protect against zero-day exploits targeting widely used applications in enterprise networks.
The exploitation chain typically involves crafting a malicious PDF document that triggers the out-of-bounds read condition when processed by the vulnerable Acrobat Reader version. This attack can result in memory corruption that allows attackers to extract system information, potentially including user credentials or other sensitive data stored in memory. The vulnerability's classification as a remote code execution risk underscores the need for comprehensive network security monitoring and endpoint protection measures. Organizations should also consider implementing application whitelisting policies that restrict execution of untrusted PDF files and maintain detailed audit logs of PDF processing activities to detect potential exploitation attempts.