CVE-2023-21608: Adobe Acrobat DC RCE Vulnerability

CVE-2023-21608 Overview

CVE-2023-21608 is a Use After Free vulnerability affecting Adobe Acrobat Reader and Adobe Acrobat products across multiple versions. This memory corruption flaw allows attackers to achieve arbitrary code execution in the context of the current user when a victim opens a specially crafted malicious PDF file. The vulnerability has been confirmed as actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.

Critical Impact

Successful exploitation enables arbitrary code execution with the privileges of the current user. This vulnerability is actively exploited in the wild and has been added to CISA's Known Exploited Vulnerabilities catalog, requiring immediate attention.

Affected Products

• Adobe Acrobat DC (Continuous) versions 22.003.20282 and earlier
• Adobe Acrobat Reader DC (Continuous) versions 22.003.20281 and earlier
• Adobe Acrobat (Classic) version 20.005.30418 and earlier
• Adobe Acrobat Reader (Classic) version 20.005.30418 and earlier
• Affected on Microsoft Windows and Apple macOS platforms

Discovery Timeline

• 2023-01-18 - CVE-2023-21608 published to NVD
• 2025-10-23 - Last updated in NVD database

Technical Details for CVE-2023-21608

Vulnerability Analysis

CVE-2023-21608 is a Use After Free (CWE-416) vulnerability in Adobe Acrobat and Acrobat Reader. Use After Free vulnerabilities occur when a program continues to use a pointer after the memory it references has been freed. In this case, the vulnerability allows an attacker to manipulate memory in such a way that when the freed memory is subsequently accessed, it can lead to arbitrary code execution.

The exploitation requires user interaction—specifically, a victim must open a malicious PDF document. Once opened, the attacker-controlled content triggers the Use After Free condition, allowing execution of arbitrary code with the same privileges as the current user. Given that PDF viewers are commonly used to open documents from untrusted sources, this vulnerability presents a significant attack surface for targeted attacks, phishing campaigns, and document-based malware delivery.

Root Cause

The root cause of this vulnerability lies in improper memory management within Adobe Acrobat and Reader's PDF parsing and rendering engine. When processing certain PDF structures or JavaScript objects, the application frees memory that is subsequently referenced by another part of the code. This dangling pointer condition can be exploited by carefully crafting PDF content that controls what data occupies the freed memory location, ultimately enabling code execution.

Attack Vector

The attack vector is local, requiring the attacker to deliver a malicious PDF file to the victim. Common delivery methods include:

• Email attachments containing weaponized PDF documents
• Drive-by downloads from compromised or malicious websites
• Social engineering tactics to convince users to open malicious files
• Supply chain attacks where legitimate documents are modified

Once the victim opens the malicious PDF in an affected version of Adobe Acrobat or Reader, the Use After Free condition is triggered. The attacker's payload then executes with the privileges of the user running the application, potentially leading to complete system compromise, data theft, or lateral movement within an organization.

The vulnerability mechanism involves memory corruption through improper object lifecycle management. When certain PDF objects are processed, the application deallocates memory while retaining references to it. Subsequent operations that access these dangling pointers can be manipulated by an attacker who has placed controlled data in the freed memory region. For detailed technical analysis, refer to the Adobe Security Bulletin APSB23-01.

Detection Methods for CVE-2023-21608

Indicators of Compromise

• Unexpected crashes or abnormal behavior in Adobe Acrobat or Reader processes
• Suspicious PDF files with obfuscated JavaScript or unusual object structures
• Child processes spawned by AcroRd32.exe or Acrobat.exe that are atypical (e.g., cmd.exe, powershell.exe)
• Network connections initiated by Adobe Acrobat processes to unknown or suspicious destinations

Detection Strategies

• Monitor process creation events for Adobe Acrobat/Reader spawning shell interpreters or unexpected child processes
• Implement endpoint detection rules for memory corruption exploitation patterns in PDF reader applications
• Deploy behavioral analysis to detect post-exploitation activities following PDF document access
• Use sandboxing solutions to analyze PDF attachments before delivery to end users

Monitoring Recommendations

• Enable enhanced logging for endpoint detection and response (EDR) solutions monitoring Adobe product behavior
• Implement file integrity monitoring for Adobe Acrobat installation directories
• Configure SIEM alerts for suspicious process trees involving Adobe Acrobat or Reader
• Monitor for known exploitation patterns associated with CISA KEV-listed vulnerabilities

How to Mitigate CVE-2023-21608

Immediate Actions Required

• Update Adobe Acrobat and Reader to the latest patched versions immediately
• Enable Protected Mode and Enhanced Security settings in Adobe Acrobat and Reader
• Implement application control policies to restrict PDF document sources
• Educate users about the risks of opening PDF attachments from untrusted sources

Patch Information

Adobe has released security updates addressing this vulnerability in Security Bulletin APSB23-01. Organizations should update to the following versions or later:

• Adobe Acrobat DC (Continuous): Update to version 22.003.20310 or later
• Adobe Acrobat Reader DC (Continuous): Update to version 22.003.20310 or later
• Adobe Acrobat 2020 (Classic): Update to version 20.005.30436 or later
• Adobe Acrobat Reader 2020 (Classic): Update to version 20.005.30436 or later

Due to active exploitation, CISA has mandated federal agencies to remediate this vulnerability. All organizations are strongly encouraged to prioritize patching given the confirmed in-the-wild exploitation.

Workarounds

• Enable Protected View for files originating from potentially unsafe locations
• Configure Adobe Reader to open PDFs in a sandboxed environment
• Implement Group Policy settings to disable JavaScript in PDF documents if not required
• Consider using alternative PDF readers with enhanced security features until patching is complete

# Windows Registry configuration to enable Protected View
reg add "HKCU\Software\Adobe\Acrobat Reader\DC\TrustManager" /v bEnableProtectedModeAtStartup /t REG_DWORD /d 1 /f
reg add "HKCU\Software\Adobe\Acrobat Reader\DC\TrustManager" /v iProtectedView /t REG_DWORD /d 2 /f