CVE-2020-29075: Adobe Acrobat Information Disclosure Flaw

CVE-2020-29075 Overview

CVE-2020-29075 is an information exposure vulnerability affecting Adobe Acrobat Reader DC and related products. This vulnerability enables an attacker to initiate DNS interactions that can track whether a user has opened or closed a PDF file when the document is loaded from the filesystem. The attack does not trigger any user prompt, making it particularly concerning for privacy and user tracking scenarios.

Critical Impact

Attackers can silently track PDF document interactions through DNS requests, enabling surveillance of user document activity without explicit consent or notification.

Affected Products

• Adobe Acrobat DC (Continuous) versions prior to 2020.013.20066
• Adobe Acrobat Reader DC (Continuous) versions prior to 2020.013.20066
• Adobe Acrobat (Classic 2020) versions prior to 2020.001.30010
• Adobe Acrobat Reader (Classic 2020) versions prior to 2020.001.30010
• Adobe Acrobat (Classic 2017) versions prior to 2017.011.30180
• Adobe Acrobat Reader (Classic 2017) versions prior to 2017.011.30180
• Affects Windows and macOS platforms

Discovery Timeline

• 2021-02-23 - CVE-2020-29075 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-29075

Vulnerability Analysis

This information exposure vulnerability (CWE-200) combined with improper input validation (CWE-20) allows attackers to embed malicious content within PDF documents that triggers external DNS requests when the document is opened. The vulnerability exploits the way Adobe Acrobat and Acrobat Reader process PDF files loaded from the local filesystem.

When a victim opens a crafted PDF document, the application initiates network requests to attacker-controlled infrastructure without displaying any security prompts to the user. This silent network activity can be leveraged to confirm document access, track user behavior, and potentially gather additional information about the target environment through DNS callback mechanisms.

Root Cause

The root cause stems from improper input validation in Adobe Acrobat's PDF processing engine. The application fails to adequately restrict or prompt users when PDF documents attempt to initiate external network connections. Specifically, when PDF files are loaded from the local filesystem, certain embedded elements can trigger DNS lookups to arbitrary domains controlled by attackers. This behavior bypasses expected security controls that would normally alert users to potentially dangerous network activity.

Attack Vector

The attack is delivered through a network-based vector requiring user interaction. An attacker must craft a malicious PDF document and distribute it to potential victims through email, websites, or other distribution channels.

The attack flow follows this pattern:

1. Attacker creates a PDF document with embedded elements designed to trigger DNS requests
2. The crafted PDF is delivered to the victim through phishing, malicious websites, or file sharing
3. Victim downloads and opens the PDF file from their local filesystem
4. Adobe Acrobat processes the document and silently initiates DNS requests to attacker-controlled domains
5. The attacker's DNS infrastructure logs the request, confirming the victim opened the document
6. Additional tracking can determine when the document is closed

This technique is commonly used in targeted phishing campaigns to confirm email delivery and document access before launching subsequent attacks.

Detection Methods for CVE-2020-29075

Indicators of Compromise

• Unexpected DNS queries originating from Adobe Acrobat processes (Acrobat.exe or AcroRd32.exe)
• Network connections to suspicious or unknown domains immediately after opening PDF files
• DNS query patterns that correlate with PDF document opening and closing events
• Unusual outbound network activity from PDF reader applications

Detection Strategies

• Monitor DNS query logs for requests initiated by Adobe Acrobat processes to external domains
• Implement network traffic analysis to detect PDF-triggered callbacks to unrecognized infrastructure
• Deploy endpoint detection rules that alert on Adobe Acrobat initiating network connections to newly observed domains
• Use sandbox analysis for PDF documents to identify potential tracking mechanisms before user interaction

Monitoring Recommendations

• Enable DNS logging on endpoint systems and correlate with process execution events
• Configure network security monitoring to flag outbound connections from PDF reader applications
• Implement behavioral analysis for Adobe Acrobat to detect anomalous network activity patterns
• Establish baseline network behavior for PDF applications to identify deviations

How to Mitigate CVE-2020-29075

Immediate Actions Required

• Update Adobe Acrobat DC to version 2020.013.20066 or later (Continuous track)
• Update Adobe Acrobat to version 2020.001.30010 or later (Classic 2020 track)
• Update Adobe Acrobat to version 2017.011.30180 or later (Classic 2017 track)
• Review and apply security settings to restrict PDF network access capabilities
• Educate users about the risks of opening PDF documents from untrusted sources

Patch Information

Adobe has released security patches addressing this vulnerability in Adobe Security Bulletin APSB20-75. Organizations should apply these updates through their standard software update mechanisms or download the latest versions directly from Adobe's website. The patch restricts the ability of PDF documents to initiate DNS interactions without user awareness.

Workarounds

• Configure Adobe Acrobat's Protected Mode to restrict network access from PDF documents
• Use Group Policy or enterprise management tools to disable external URL access in PDF files
• Implement network-level controls to block outbound DNS requests from Adobe Acrobat processes to untrusted domains
• Consider using alternative PDF readers with more restrictive security defaults for high-risk environments

For enterprise environments, administrators can configure Enhanced Security settings in Adobe Acrobat through Group Policy templates or the Adobe Customization Wizard to restrict external content loading and network access from PDF documents.