CVE-2026-34626: Adobe Acrobat Information Disclosure Flaw

CVE-2026-34626 Overview

CVE-2026-34626 is a Prototype Pollution vulnerability affecting Adobe Acrobat Reader that enables arbitrary file system read operations in the context of the current user. The vulnerability stems from Improperly Controlled Modification of Object Prototype Attributes (CWE-1321), which allows attackers to manipulate JavaScript object prototypes within maliciously crafted PDF documents.

Exploitation requires user interaction—specifically, a victim must open a malicious PDF file. Once triggered, the vulnerability can expose sensitive files accessible to the current user, potentially including configuration files, credentials, and other confidential data stored on the local file system.

Critical Impact

Successful exploitation allows attackers to read arbitrary files from the victim's file system, potentially exposing sensitive data, credentials, and configuration files when a user opens a malicious PDF document.

Affected Products

• Adobe Acrobat versions 26.001.21411 and earlier
• Adobe Acrobat DC (Continuous track) versions 24.001.30360, 24.001.30362 and earlier
• Adobe Acrobat Reader DC (Continuous track) versions 24.001.30360, 24.001.30362 and earlier

Discovery Timeline

• 2026-04-14 - CVE-2026-34626 published to NVD
• 2026-04-16 - Last updated in NVD database

Technical Details for CVE-2026-34626

Vulnerability Analysis

This Prototype Pollution vulnerability exists in Adobe Acrobat Reader's JavaScript engine implementation. Prototype Pollution occurs when an attacker can inject properties into existing JavaScript object prototypes, such as Object.prototype. In the context of PDF documents, Adobe Acrobat supports embedded JavaScript for interactive features, and this implementation fails to properly sanitize or restrict modifications to base object prototypes.

The vulnerability allows an attacker to pollute JavaScript prototypes in a way that subsequently enables arbitrary file system read operations. This is particularly dangerous because PDF files are commonly exchanged in business contexts and users may not suspect malicious content in document files.

The local attack vector combined with the requirement for user interaction means social engineering plays a role in successful exploitation. An attacker would need to convince a target to open a crafted PDF file, which could be delivered via email, file sharing services, or compromised websites.

Root Cause

The root cause is an Improperly Controlled Modification of Object Prototype Attributes (CWE-1321) in the JavaScript engine used by Adobe Acrobat Reader. The application fails to implement proper prototype pollution protections when processing JavaScript within PDF documents. This allows malicious JavaScript code embedded in a PDF to modify base object prototypes, which can then be leveraged to bypass security controls and access the local file system.

Modern JavaScript engines in security-sensitive contexts should implement prototype freezing, input validation on property assignments, and restrictions on __proto__ and constructor.prototype modifications. The absence of these protections enables this vulnerability.

Attack Vector

The attack requires local access in the form of user interaction with a malicious file. An attacker crafts a PDF document containing malicious JavaScript that exploits the prototype pollution vulnerability. The attack sequence proceeds as follows:

1. Attacker creates a PDF with embedded JavaScript containing prototype pollution payloads
2. The PDF is distributed to the target via email, download links, or other delivery methods
3. Victim opens the PDF in a vulnerable version of Adobe Acrobat Reader
4. The embedded JavaScript executes and pollutes object prototypes
5. The polluted prototypes enable the attacker's code to read arbitrary files from the user's file system
6. Sensitive file contents are exfiltrated or used for further attack stages

The vulnerability enables high confidentiality impact with the ability to read files outside the intended scope, affecting the security scope (Changed scope in CVSS). However, it does not provide write access to the file system or enable denial of service.

Detection Methods for CVE-2026-34626

Indicators of Compromise

• PDF files containing suspicious JavaScript with references to __proto__, constructor.prototype, or Object.prototype
• Unexpected file system read operations initiated by Adobe Acrobat Reader processes
• JavaScript code in PDFs attempting to access file paths outside normal document operations
• Acrobat Reader process accessing sensitive configuration files or credential stores

Detection Strategies

• Monitor Adobe Acrobat Reader processes for unusual file system access patterns, particularly reads of sensitive system or user files
• Implement endpoint detection rules to flag PDF files containing JavaScript that manipulates prototype chains
• Deploy content inspection on email gateways to detect potentially malicious PDFs before delivery to users
• Use behavioral analysis to identify Acrobat Reader accessing files inconsistent with normal PDF rendering operations

Monitoring Recommendations

• Enable enhanced logging for Adobe Acrobat Reader file system access on endpoints
• Configure SIEM rules to correlate PDF file opens with subsequent suspicious file reads by the same process
• Monitor for unusual outbound data transfers following PDF file access
• Implement file integrity monitoring on sensitive files that should not be accessed by PDF reader applications

How to Mitigate CVE-2026-34626

Immediate Actions Required

• Update Adobe Acrobat and Acrobat Reader to the latest patched versions immediately
• Educate users to avoid opening PDF files from untrusted or unexpected sources
• Consider implementing application control policies to restrict JavaScript execution in PDF files
• Deploy endpoint protection solutions capable of detecting prototype pollution attacks

Patch Information

Adobe has released security updates addressing this vulnerability. Organizations should update to the following minimum versions or later:

• Adobe Acrobat (Classic track): Versions after 26.001.21411
• Adobe Acrobat DC (Continuous track): Versions after 24.001.30362
• Adobe Acrobat Reader DC (Continuous track): Versions after 24.001.30362

Detailed patch information is available in the Adobe Security Bulletin APSB26-44. Organizations running affected versions on Windows or macOS should prioritize these updates.

Workarounds

• Disable JavaScript in Adobe Acrobat Reader via Edit > Preferences > JavaScript > uncheck "Enable Acrobat JavaScript"
• Implement Protected View for all PDF files from external sources (Edit > Preferences > Security (Enhanced) > Enable Protected View)
• Use alternative PDF readers for untrusted documents until patches are applied
• Configure email security gateways to strip JavaScript from incoming PDF attachments or quarantine PDFs with embedded scripts

# Registry configuration to disable JavaScript in Acrobat Reader DC (Windows)
# Run as Administrator
reg add "HKLM\SOFTWARE\Policies\Adobe\Acrobat Reader\DC\FeatureLockDown" /v bDisableJavaScript /t REG_DWORD /d 1 /f

# For Adobe Acrobat DC
reg add "HKLM\SOFTWARE\Policies\Adobe\Adobe Acrobat\DC\FeatureLockDown" /v bDisableJavaScript /t REG_DWORD /d 1 /f