CVE-2021-28551
📋 TL;DR
CVE-2021-28551 is an out-of-bounds read vulnerability in Adobe Acrobat Reader DC that could allow arbitrary code execution when a user opens a malicious PDF file. Attackers can exploit this to run code with the victim's privileges, requiring user interaction through file opening. Users of affected Adobe Acrobat Reader DC versions are at risk.
💻 Affected Systems
- Adobe Acrobat Reader DC
📦 What is this software?
Acrobat by Adobe
Acrobat by Adobe
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via arbitrary code execution leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Malicious code execution leading to credential theft, data exfiltration, or lateral movement within the network.
If Mitigated
Limited impact with proper application sandboxing and user privilege restrictions, potentially containing the exploit to the application context.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file). No public proof-of-concept was available at disclosure time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2021.001.20155 (for 2021 track), 2020.001.30025 (for 2020 track), 2017.011.30196 (for 2017 track) - update to versions after these
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb21-29.html
Restart Required: Yes
Instructions:
1. Open Adobe Acrobat Reader DC. 2. Go to Help > Check for Updates. 3. Follow prompts to install available updates. 4. Restart the application when prompted.
🔧 Temporary Workarounds
Disable JavaScript in Adobe Reader
allPrevents JavaScript-based exploitation vectors that might be used in conjunction with this vulnerability
Edit > Preferences > JavaScript > Uncheck 'Enable Acrobat JavaScript'
Use Protected View
allOpen untrusted PDFs in Protected View mode to limit potential damage
File > Open > Select 'Protected View' option when opening files
🧯 If You Can't Patch
- Restrict PDF file opening to trusted sources only using application control policies
- Implement network segmentation to limit lateral movement if exploitation occurs
🔍 How to Verify
Check if Vulnerable:
Check Adobe Acrobat Reader DC version via Help > About Adobe Acrobat Reader DCCheck Version:
On Windows: wmic product where name="Adobe Acrobat Reader DC" get versionVerify Fix Applied:
Verify version is newer than affected versions: 2021.001.20155, 2020.001.30025, or 2017.011.30196📡 Detection & Monitoring
Log Indicators:
- Adobe Reader crash logs with memory access violations
- Unexpected child processes spawned from AcroRd32.exe
Network Indicators:
- Outbound connections from Adobe Reader process to unexpected destinations
- DNS queries for suspicious domains from user workstations
SIEM Query:
process_name:AcroRd32.exe AND (event_id:1000 OR event_id:1001) OR parent_process:AcroRd32.exe AND process_creation