CVE-2025-29815 - Exploiting Use-After-Free in Microsoft Edge (Chromium-Based) for Remote Code Execution

In early 2025, security researchers uncovered a critical vulnerability in Microsoft Edge (Chromium-based), tracked as CVE-2025-29815. This "use-after-free" flaw can allow an attacker to run malicious code on a victim’s system—simply by getting them to visit a specially crafted website. Let’s break down what this means, how it happens, and how attackers can exploit it, with practical code snippets and useful resources.

What is a Use-After-Free Vulnerability?

A use-after-free bug occurs when an application continues to use a part of memory after it has been "freed" (or released). In C++-based browsers like Chromium, freed memory can potentially be reallocated or overwritten. If an attacker controls that memory, they can take over execution flow.

Breaking Down CVE-2025-29815

Summary:
A use-after-free vulnerability exists in Microsoft Edge (Chromium-based) versions prior to build 120..240.72. It allows a remote attacker—who tricks a user into visiting a malicious web page—to execute arbitrary code with the context of the user.

Impact:

Full remote code execution (RCE)

- Attacker can control the victim’s browser/device

User only needs to visit a specially crafted webpage

References:
- Microsoft Security Advisory
- Chromium Bugs
- Edge Release Notes

How the Vulnerability Can Be Triggered

The root cause of CVE-2025-29815 lies in Edge’s handling of certain DOM objects. If an attacker triggers a sequence such as creating, deleting, and then reusing a DOM object (like a div or a JavaScript object), the browser could reuse freed memory, allowing the attacker to inject malicious code.

Proof-of-Concept (PoC) Exploit (for Research Use Only!)

The following is a generic PoC. The real exploit will target a specific object and its event handler, but the basic idea is:

let victim;
let buffer = [];

function triggerUAF() {
    // Step 1: Create and attach victim object
    victim = document.createElement('div');
    document.body.appendChild(victim);

    // Step 2: Free the victim object's memory
    document.body.removeChild(victim);

    // Step 3: Fill memory with attacker-controlled data
    for(let i = ; i < 10000; i++) {
        let obj = document.createElement('textarea');
        obj.value = "A".repeat(100);
        buffer.push(obj);
    }

    // Step 4: Force browser to use freed memory
    // This is browser and bug specific, but typically involves:
    try {
        victim.addEventListener('click', function(){ alert('exploit') });
        victim.click();
    } catch(e) {
        // Handle error
    }
}

window.onload = triggerUAF;

Note: The actual exploit would require deep knowledge of how Edge allocates memory internally, but this code demonstrates the general principle of inducing a use-after-free situation, and controlling memory allocation afterwards.

Exploit Details: Remote Code Execution

Once a use-after-free is triggered, the attacker can "spray" memory with specially crafted objects (like arrays or strings containing their exploit code). When the browser uses the dangling pointer, it will execute attacker-supplied code instead of legitimate application logic.

The site runs the exploit, causing the browser to crash—or worse, run malware.

- Attacker now has control over the victim’s browser session, files, or even the whole computer, depending on system protections.

Protection and Mitigation

Microsoft has released a patch—make sure your Edge browser is updated!

References & Further Reading

- Microsoft Edge Security Update Guide - CVE-2025-29815
- Chromium Use-After-Free Exploitation Guide (Google Project Zero)
- Microsoft Edge Release Notes

Summary

CVE-2025-29815 is a dangerous, remotely exploitable bug in Microsoft Edge (Chromium-based). By exploiting a use-after-free flaw, attackers can take over users' browsers (and possibly computers) over the network. The best defense is to update as soon as possible and practice safe browsing habits. Security researchers and developers should always be wary of memory management bugs in any widely used software.

Timeline

Published on: 04/04/2025 01:15:39 UTC
Last modified on: 06/04/2025 17:53:33 UTC