CVE-2021-28550
📋 TL;DR
CVE-2021-28550 is a use-after-free vulnerability in Adobe Acrobat Reader DC that allows arbitrary code execution when a user opens a malicious PDF file. It affects users of Acrobat Reader DC across multiple versions on various operating systems, requiring user interaction to exploit.
💻 Affected Systems
- Adobe Acrobat Reader DC
📦 What is this software?
Acrobat by Adobe
Acrobat by Adobe
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains full control of the victim's system by executing arbitrary code in the context of the current user, potentially leading to data theft, ransomware deployment, or further network compromise.
Likely Case
Targeted attacks via phishing emails with malicious PDF attachments result in malware installation or credential harvesting on individual user systems.
If Mitigated
With proper patching and security controls, the risk is minimized to isolated incidents with limited impact, such as blocked file execution or contained malware.
🎯 Exploit Status
Exploitation is straightforward via malicious PDF files, with public proof-of-concept code available and confirmed use in attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2021.001.20155 or later for 2021 versions, 2020.001.30025 or later for 2020 versions, 2017.011.30199 or later for 2017 versions
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 the latest version. 4. Restart the application and system if required.
🔧 Temporary Workarounds
Disable JavaScript in Adobe Reader
allPrevents exploitation by disabling JavaScript, which may be used in the attack chain, but could affect PDF functionality.
In Adobe Reader, go to Edit > Preferences > JavaScript, then uncheck 'Enable JavaScript'.
Block PDF files from untrusted sources
allUse email filtering or endpoint controls to block or sandbox PDF attachments from unknown senders.
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized executables from running.
- Use network segmentation and least privilege access to limit potential lateral movement if exploited.
🔍 How to Verify
Check if Vulnerable:
Check the Adobe Reader version via Help > About Adobe Acrobat Reader DC and compare to affected versions listed in the advisory.Check Version:
On Windows: wmic product where name='Adobe Acrobat Reader DC' get version; on macOS: /Applications/Adobe\ Acrobat\ Reader\ DC.app/Contents/Info.plist | grep -A1 CFBundleShortVersionStringVerify Fix Applied:
Verify the version is updated to a patched version (e.g., 2021.001.20155 or higher) and ensure no suspicious PDF files have been opened.📡 Detection & Monitoring
Log Indicators:
- Unusual process creation from Adobe Reader (e.g., cmd.exe, powershell.exe), crash logs in Adobe Reader event logs.
Network Indicators:
- Outbound connections to unknown IPs initiated by Adobe Reader process.
SIEM Query:
Process creation where parent process contains 'AcroRd32.exe' and command line includes suspicious strings like 'powershell' or 'cmd'.