In mid-2022, a significant security flaw (CVE-2022-1861) was discovered and disclosed in Google Chrome running on Chrome OS systems, up to version 102..5005.61. This vulnerability is categorized as a use-after-free flaw, specifically within the Sharing component. This post will break down what the vulnerability is, how it can be exploited, and why it's important to keep browsers up to date. We'll also include references and a simple code snippet to illustrate how use-after-free bugs can be abused.

What is CVE-2022-1861?

CVE-2022-1861 relates to a use-after-free condition in the Sharing functionality of Google Chrome on Chrome OS. It allowed a remote attacker—someone not local to your machine—to potentially corrupt memory in the heap area, by convincing a user to perform certain actions (e.g., clicking on a crafted website or popup).

A use-after-free (UAF) happens when code continues to access a memory area after it has been freed or deleted, which means this memory could be altered or hijacked by malicious code.

The Technical Details

The bug existed in the way Chrome handled the life cycle of certain objects involved in the Sharing feature. If a user could be enticed to perform certain clicks or interactions, the underlying code might free a memory object, but then later try to use it again, resulting in undefined behavior.

While the full technical proof-of-concept for the exact Chrome Sharing UAF hasn't been made public by Google due to responsible disclosure, the pattern is similar to other use-after-free bugs in C++ and browser engines.

Sample Code: General Use-After-Free in C++

Here's a simple C++ example (not Chrome code, but simplified for understanding). Imagine the flow where an object is deleted but still referenced:

#include <iostream>

class SharedObject {
public:
    void doSomething() {
        std::cout << "Using shared object!" << std::endl;
    }
};

int main() {
    SharedObject* obj = new SharedObject();
    delete obj;          // Memory is freed here
    obj->doSomething();  // Use-after-free: unsafe!
    return ;
}

In this example, calling doSomething() after delete may cause a crash, or worse, allow for heap memory corruption if an attacker can allocate their own data at that position.

How Attackers Exploit This (Simplified Steps)

1. Victim visits malicious page: The attacker tricks a user into visiting a page or opening a sharing action.
2. Triggers buggy use-after-free logic: Crafted scripts or interactions force Chrome to free a memory object, but a callback or event soon after still tries to use it.
3. Heap is controlled: The attacker may use heap spraying techniques to place controlled data in freed memory.
4. Corrupts execution flow: When Chrome uses the dangling pointer, attacker-controlled data is accessed, potentially allowing code execution or crashing the process.

Here is an abstract snippet showing JS heap spray (not directly Chrome, but general browser heap spray):

// Heap spraying with JavaScript to fill memory with malicious data
var spray = [];
for (var i = ; i < 10000; i++) {
    spray.push("EXPLOIT" + i + Math.random());
}

In a real attack, after freeing the vulnerable object, this spray may land attacker-controlled strings in its place.

References

- Google Chromium Security Advisory for CVE-2022-1861
- NIST National Vulnerability Database entry - CVE-2022-1861
- Chrome UAF vulnerabilities and exploitation techniques (general piece by Project Zero)

Update Chrome OS and Chrome Browser: This issue was patched in version 102..5005.61 and later.

- Be cautious with suspicious links: Don’t click links or engage with popups from unknown sources.

Conclusion

CVE-2022-1861 is a clear example of how memory management issues in widely-used software like Google Chrome can lead to real security risks. Use-after-free bugs are especially dangerous as they can allow an attacker to subvert memory protections and execute code on a victim's device. The fix is simple: keep your browser and Chrome OS updated, and don’t ignore security updates.

For more technical readers, inspecting open-source Chrome code and security patches can provide deeper insights into how such bugs are located and patched. Remember: a single click on a malicious webpage can be enough to compromise your device if you’re running outdated software!

Timeline

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