CVE-2022-28269 - Exploiting a Use-After-Free in Acrobat Reader DC (Simple Walkthrough & Analysis)

In April 2022, Adobe published a critical security bulletin about CVE-2022-28269, a use-after-free vulnerability in Acrobat Reader DC. If you’re looking for a simple, straightforward explanation of what this bug is, why it matters, and how it can be exploited, you’re in the right place. Let’s dig in!

What is CVE-2022-28269?

CVE-2022-28269 is a use-after-free vulnerability found in how Acrobat Reader DC processed Annotation objects inside PDF files. A “use-after-free” means the program accesses memory that’s already been released, which can give hackers a way to run their own code.

Acrobat Reader 2017 17.012.30205 and earlier

If you’re using any of these, you should update *right now*.

The victim opens the PDF in Acrobat Reader DC.

4. The crafted annotation triggers the use-after-free, corrupting memory and potentially giving the attacker control of the victim’s computer.

Note: Attacks require user interaction — you have to open the malicious file yourself.

When Acrobat Reader parses a PDF, it handles annotation objects like so (simplified pseudocode)

// Simplified pseudocode
Annotation* annotation = new Annotation();
renderAnnotation(annotation);
delete annotation; // Memory is freed

// Later, code mistakenly uses the freed annotation pointer
annotation->draw(); // --- use-after-free! ---

So if a hacker can influence the way annotations are handled (via a malformed PDF), they could trigger draw() on already-freed memory, which opens the door for code execution.

Proof-of-Concept (PoC) Snippet

Below is a simplified PoC (for educational purposes only) that shows how an attacker could craft a PDF with a dangerous annotation:

%PDF-1.7
1  obj
<< /Type /Catalog /Pages 2  R >>
endobj
2  obj
<< /Type /Pages /Kids [3  R] /Count 1 >>
endobj
3  obj
<< /Type /Page /Parent 2  R /Annots [4  R] >>
endobj
4  obj
<< /Type /Annot /Subtype /Text
   /Rect [100 100 200 200]
   /Contents (Trigger use-after-free here)
   /SomeEvilKey << ... attacker controls this ... >>
>>
endobj
xref
 5
000000000 65535 f 
000000001 00000 n 
0000000062 00000 n 
0000000122 00000 n 
000000019 00000 n 
trailer
<< /Root 1  R /Size 5 >>
startxref
276
%%EOF

A real attacker would use /SomeEvilKey with deeply nested dictionaries or references that mess with Acrobat Reader’s annotation lifecycle, forcing reuse of freed memory.

Execute arbitrary code (run whatever they want as the user)

All this is possible just by you opening a poisoned PDF. No admin rights needed.

Official References & Resources

- Adobe Security Bulletin APSB22-16
- NIST NVD Entry for CVE-2022-28269
- Exploit DB PoC (if available)

Mitigation

1. Update ASAP:
Patch to at least version 22.001.20091 (or later).

2. Disable JavaScript:
Disable JavaScript in Acrobat if you don't need it (it can make exploitation easier).

3. Be suspicious:
Don’t open PDFs from people you don’t trust.

Conclusion

CVE-2022-28269 is a serious flaw in Acrobat Reader DC, and demonstrates how complex file formats like PDF can hide dangerous surprises. Exploitation is possible with a simple PDF and user interaction. Always keep your software updated!

*If you’re a developer or sysadmin, consider running Reader in sandboxed environments and deploying updates enterprise-wide.*

If you found this guide useful, please share it with your team or friends before any more malicious PDFs make the rounds.

*Written exclusively for you, June 2024. Stay secure!*

Timeline

Published on: 05/11/2022 18:15:00 UTC
Last modified on: 05/20/2022 17:37:00 UTC