In early 2022, a severe vulnerability, tracked as CVE-2022-28838, was found and patched in Adobe Acrobat and Acrobat Pro DC. This bug affects versions 22.001.2011x (and earlier), 20.005.3033x (and earlier), and 17.012.3022x (and earlier). At its core, this is a "use-after-free" vulnerability inside the PDF processing engine, which opens the door for attackers to run arbitrary code on a victim’s system. All it needs is for a user to open a booby-trapped PDF file.

If you’re using an outdated Acrobat release, your system is at high risk—especially since malicious PDFs can be steganographically smuggled in email or downloads.

This is an exclusive technical rundown—in simple terms—on how CVE-2022-28838 works, with fresh code snippets and real-world exploitation details.

What Is a Use-After-Free Vulnerability?

A *use-after-free* is when a program tries to use memory after it has already released (“freed”) that memory. In C++, for example, using a pointer to an object that’s already been deleted can let attackers mess directly with memory. If attackers gain control of what's just been freed, they can inject their own code or force the program to crash.

How Does CVE-2022-28838 Work in Acrobat?

The actual bug lies in how Acrobat manages objects inside a PDF. When Acrobat opens a compromised PDF, it might release memory for an internal object (say, a form field or media object), but then try to use it—because of how complex PDFs can reference the same object in different parts of the structure.

With careful PDF crafting, attackers can control *when* and *what* memory Acrobat uses after it's been freed, letting them insert malicious code that Acrobat will unwittingly run.

(e.g., form field actions, custom annotations)

3. Acrobat frees a memory chunk but then tries to use it again due to the way the PDF is constructed.

Acrobat runs the attacker's code under the current user’s permissions.

Important: The exploit cannot trigger *automatically* — it needs user interaction (like double-clicking or opening with "File > Open").

Basic Exploit Code Snippet (Proof-of-Concept)

*Below is a pseudo-PDF JavaScript exploitation trigger showing how an attacker might go about it—do not use on production or live systems:*

// Part of a crafted PDF file, embedded in /OpenAction or a Form Event
this.getAnnots()[].destroy();  // Frees a critical object
// Then, trigger use-after-free
var leaked = this.getAnnots()[].contents;  
// At this point, 'leaked' can be anything the attacker injected into the freed slot

In a real attack, the exploit would be much more complex—mixing low-level PDF commands to orchestrate memory layout:

1  obj
  << /Type /Annot /Subtype /Text /Contents (Malicious Data) >>
endobj
...
2  obj
  << /OpenAction << /S /JavaScript /JS (app.alert(this.getAnnots()[].destroy());) >> >>
endobj


*Note: This is a representation; real exploits manipulate exact memory layout and may use advanced heap spraying.*

Real-World Exploit Details

- Delivery: Most real attacks would deliver the PDF through spear-phishing emails, instant messages, or malicious websites.
- Payload: After the use-after-free is triggered, attackers would inject shellcode (binary code), commonly aiming for a reverse shell or other malware downloaders.
- Post-Exploitation: The attacker now controls Acrobat with the victim's user privileges, able to steal files, watch keystrokes, or move deeper into the network.

How to Stay Safe

- Update Acrobat Immediately: Get the latest patches from Adobe.
- Disable JavaScript in Acrobat: Go to *Preferences > JavaScript* and uncheck "Enable Acrobat JavaScript."

References & Further Reading

- Adobe Security Bulletin APSB22-16
- NIST CVE-2022-28838 Record
- Project Zero: Attacking PDF Readers (General PDF Exploitation) *(for deeper insight into PDF attacks)*

Final Thoughts

CVE-2022-28838 is a textbook example of why use-after-free bugs are so dangerous—especially in software as common as Adobe Acrobat. Anyone handling sensitive or critical documents should *ensure* they’re running the latest version, and treat email attachments with extra caution.

*Stay updated and stay safe—today’s PDFs are not just documents, they’re potential attack vectors.*

Timeline

Published on: 05/11/2022 18:15:00 UTC
Last modified on: 08/19/2022 23:15:00 UTC