CVE-2026-34621 : Adobe Acrobat 2026 Prototype Pollution & JS Injection Chain

May 12, 2026 · View on GitHub

Overview

This repository contains research material and proof-of-concept code developed during the analysis of the 2026 Adobe Acrobat Reader in-the-wild exploit chain involving:

  • Prototype Pollution
  • Internal JavaScript Injection
  • Trusted Workflow Abuse
  • Patch Diffing
  • Privileged JavaScript Execution

The research focuses on understanding the vulnerability chain used by malicious PDF documents and reverse engineering the fixes introduced by Adobe across multiple patches.

This work was created for:

  • vulnerability research,
  • reverse engineering,
  • malware analysis,
  • and educational purposes.

Vulnerabilities Analyzed

  • CVE-2026-34621
  • CVE-2026-34622
  • CVE-2026-34626

Affected components include:

  • ANFancyAlertImpl()
  • SilentDocCenterLogin()
  • ANShareFile()
  • collaboration workflows inside Adobe Acrobat Reader

Research Highlights

The exploit chain combines multiple primitives:

1. JavaScript Injection Primitive

Unsafe dynamic handler construction inside:

ANFancyAlertImpl()

using:

eval(...)

allowed attacker-controlled button identifiers to inject arbitrary JavaScript into Acrobat’s internal execution flow.

2. Prototype Pollution Primitive

A vulnerable global variable resolution involving:

swConn

allowed attackers to abuse:

Object.prototype.__defineGetter__()

to redirect trusted Acrobat collaboration logic toward attacker-controlled objects.

3. Trusted Object Confusion

Trusted workflows assumed:

doc.path

was always a primitive string.

By supplying crafted objects implementing:

  • substring
  • lastIndexOf

the exploit redirected privileged execution paths into attacker-controlled callbacks.

Proof of Concept Capability

The included PoC demonstrates that the exploit chain can be abused to execute privileged JavaScript inside Adobe Acrobat Reader and perform sensitive operations normally restricted by the sandbox.

Using the trusted function registration primitive, the PoC is capable of:

  • reading files from the target machine,
  • accessing sensitive local resources,
  • and exfiltrating retrieved content through outbound requests.

During testing, the payload was used to read local system files from the victim machine and transmit their contents to the collection server implemented in:

c2.py

This behavior confirms that the exploit chain successfully crosses Acrobat’s intended trust boundaries and reaches privileged execution contexts.

Repository Contents

payload_steal.js

Research payload used during exploit reconstruction and behavioral analysis.

Contains:

  • prototype pollution logic,
  • privileged workflow abuse,
  • trusted function registration primitives,
  • local file access logic,
  • and file exfiltration routines.

CVE-2026-34621.py

Minimal PDF generator embedding external JavaScript into a PDF document.

Used during:

  • payload testing,
  • JavaScript reconstruction,
  • Acrobat behavior analysis,
  • and exploit chain validation.

Features:

  • external JS embedding,
  • automatic PDF generation,
  • OpenAction JavaScript execution.

Usage:

python3 CVE-2026-34621.py -j payload_steal.js -o exploit.pdf

c2.py

Simple HTTP collection server used during testing to observe outbound requests and payload behavior.

Used for:

  • telemetry observation,
  • chunk reconstruction,
  • and payload debugging during research.

Usage:

python3 c2.py

Default port:

45191

Patch Diffing

The repository also documents Adobe’s patch evolution across:

  • 26.001.21367
  • 26.001.21411
  • 26.001.21431

Key findings include:

  • conversion of swConn into a locally scoped variable,
  • removal of unsafe eval() usage,
  • stronger validation of trusted string-processing workflows.

Research Notes

This repository is intended for:

  • defensive security research,
  • malware analysis,
  • patch diffing,
  • and reverse engineering education.

Do not use this material against systems you do not own or explicitly have permission to test.

Related Article

Full technical write-up:

youssefazefzaf.com/posts/research-CVE-2026-34621

Acknowledgements

Additional public research and patch timeline analysis from:

  • EXPMON
  • STAR Labs
  • public malware analysis community

helped provide valuable context around the vulnerability chain and Adobe’s patching strategy.

Disclaimer

This repository is provided strictly for educational and research purposes.

The author is not responsible for misuse, unauthorized testing, or illegal activity performed using this material.