CVE-2022-1856 - Understanding and Exploiting the Chrome User Education Use-After-Free Vulnerability

Google Chrome is a pillar of web browsing for billions. Despite its strength, it’s not immune to security problems. One major bug discovered in Chrome prior to version 102..5005.61 is CVE-2022-1856—a “Use After Free” vulnerability in the browser’s User Education component. This post explores how this vulnerability works, how it was exploited, and the importance of timely Chrome updates.

What Is a Use-After-Free?

“Use after free” is a memory corruption bug. It occurs when a program frees (deletes) some memory but then continues to use it. This opens the door for attackers to “reuse” that chunk of memory to run their own code or corrupt data. It’s a common problem in complex languages like C and C++, which underpin browsers like Chrome.

Where Did It Happen in Chrome?

This bug lived in the User Education part of Chrome, which is responsible for giving users prompts and instructions about features, security, or new behaviors.

In this case, CVE-2022-1856 could be triggered if a user installed a malicious Chrome extension or was convinced to interact with the malicious extension. The extension could then manipulate the User Education code in such a way that Chrome tried to access already-freed memory, leading to heap corruption—this is technical speak for “messing up Chrome’s internal data,” potentially allowing code execution.

Who Discovered It?

This vulnerability was reported by Sergei Glazunov of Google Project Zero, one of the world’s leading browser security researchers.

- CVE Report on Chromium
- Chromium bug tracker (restricted)

Exploiting CVE-2022-1856

Here’s a simplified walk-through, using hypothetical code, illustrating how a malicious extension might have exploited this flaw.

1. Setup: Releasing Memory

Chrome’s User Education component creates pointers to data used for UI prompts. In some cases—like closing a tip—Chrome would delete this data but keep an old pointer lying around.

// Pseudocode: trigger free in User Education code
UserEducation* edu = new UserEducation();
edu->ShowTip();
// ... User clicks close or extension triggers close
delete edu;

// But Chrome still holds a pointer somewhere:
doSomething(edu->SomeField); // <-- Use after free!

2. Heap Corruption with a Malicious Extension

A rogue extension can fill the browser’s heap with crafted data right after freeing memory. The extension persuades Chrome to operate on the dangling pointer, corrupting memory or executing attacker-controlled instructions.

JavaScript Example in an Extension

// Malicious extension code, filling heap
let spray = [];
for (let i = ; i < 10000; i++) {
  spray.push(document.createElement('div'));
}
// Action triggers use-after-free in Chrome's C++ core
chrome.runtime.sendMessage({ triggerUserEducationCleanup: true });

This JavaScript spray technique tries to fill up the area of freed memory with attacker-chosen data, increasing the odds that the leftover pointer accesses it.

3. Gaining Control

If done right, the attacker can jump the browser's execution flow—maybe by overwriting a key function pointer or object, eventually running their own code in the context of the browser. This is how real-world browser escapes are built.

Real-World Impact

- Who is at risk? Anyone using Chrome before version 102 and who installs a malicious extension is vulnerable.
- How bad is it? With heap corruption, attackers can sometimes run any code they want in your browser—even take over your device in concert with other exploits.

Conclusion

CVE-2022-1856 is a classic example of how memory management bugs like use-after-free can turn simple UI features into security nightmares. The best defense: stay up-to-date, and always be skeptical of installing non-essential browser extensions. Chrome’s security team squashed this bug quickly, but the lesson remains—memory safety matters!

Timeline

Published on: 07/27/2022 22:15:00 UTC
Last modified on: 08/15/2022 11:17:00 UTC