Microsoft has patched a troubling vulnerability in its Edge browser that could allow attackers to secretly read files stored on a user’s computer. The flaw, cataloged as CVE-2026-55945, was disclosed on July 3, 2026, alongside the release of Edge version 150.0.4078.48, which contains the fix. According to Microsoft’s advisory, the issue is a race condition in the Chromium-based browser that leads to information disclosure—potentially exposing the contents of local files without the user’s knowledge.
The company has assigned a “Moderate” severity rating to the vulnerability, but security experts warn that such flaws can be combined with other exploits to cause significant damage. Here’s what you need to know, how it works, and how to protect yourself.
What exactly is the flaw?
The vulnerability resides in the core of Microsoft Edge, which shares its engine with Google Chrome. A race condition occurs when a system attempts to perform two or more operations at the same time, but the sequence of events can be manipulated to produce an unintended result. In this case, a malicious website could exploit timing differences to bypass security boundaries and capture data from local files that should be off-limits.
Microsoft’s advisory does not detail the exact files at risk, but the designation “information disclosure” typically means an attacker could read—but not modify or delete—documents, configuration files, or other sensitive data stored on the disk. Importantly, exploiting the flaw requires only that a victim visit a crafted webpage; no clicking on links or downloading files is necessary, making it a silent threat.
The vulnerability is tied directly to the Chromium project, meaning other Chromium-based browsers (like Chrome, Brave, or Opera) might have been affected, though Microsoft is the first to patch and disclose it. As of now, there is no public evidence of active exploitation, but the race to patch highlights how browser bugs can become weapons for cybercriminals.
Understanding race conditions helps grasp the risk. Think of it like two baristas trying to serve the same customer at once: the one who grabs the cup last may hand over the wrong order. In software, if an attacker can time their actions—like triggering a file read while a permission check is still underway—they can access data they shouldn’t see. These bugs are notoriously difficult to find and fix because they depend on precise system timing that may only appear under specific loads.
What this means for you
Everyday Windows users
If you use Microsoft Edge, you are at risk until you update to version 150.0.4078.48 or later. Microsoft has pushed the fix through its automatic update mechanism, so most home users will receive the patch silently. However, if you’ve disabled automatic updates or rarely restart your browser, you may be vulnerable. The simplest action is to check your Edge version immediately (instructions below) and restart the browser to apply any pending updates.
IT administrators and system managers
This vulnerability is a reminder that browsers are a primary attack vector. While the severity is deemed moderate, any local file exposure in a managed environment can lead to compliance violations involving data leaks. You should ensure that your endpoint management system (Intune, SCCM, or third-party tools) has deployed the latest Edge build. Group policies can enforce automatic updates and prevent users from delaying browser restarts. Also, consider network-level protections like web filtering to block known malicious domains, though the specific exploit vector remains unknown.
Developers
If you build web applications that integrate with Edge, this flaw doesn’t directly impact your code, but it underlines the importance of keeping test environments updated. Race condition fixes in the browser engine can alter timing behaviors, so testing your apps on the latest version is wise to catch any subtle regressions.
How we got here
Microsoft Edge’s history is intertwined with Chromium, and the browser’s rapid release cycle—with weekly security updates and frequent major version bumps—means patches often arrive swiftly. This particular vulnerability was likely discovered by an internal Microsoft team or an external researcher through the bug bounty program; the CVE was published concurrently with the fix, following responsible disclosure practices.
The timing—just days after the long July 4 holiday weekend in the US—suggests Microsoft considered the fix important enough to push out despite reduced staffing. While critical Chromium remote code execution bugs often grab headlines, information disclosure flaws like this one have been less common this year. Yet they present a clear prize for attackers seeking credentials, financial records, or corporate secrets.
Microsoft has not yet published technical details or proof-of-concept code, a standard practice to give users time to patch. However, once the patch is reverse-engineered, similar exploits could emerge for unpatched browsers. That’s why updating immediately is critical.
How to update and verify your Edge version
- Open Microsoft Edge.
- Click the three dots (…) in the top-right corner.
- Go to Help & feedback > About Microsoft Edge.
- The browser will automatically check for updates and display the version number. If it shows 150.0.4078.48 or higher, you’re safe. If not, let it download and then click Restart.
Alternatively, type edge://settings/help directly into the address bar.
For enterprise deployments, download the latest MSI or CAB files from the Microsoft Edge Business download page and distribute via your standard tools. A system restart is not required, but the browser must be relaunched.
Microsoft Edge typically updates itself in the background when you close and reopen the browser. The update mechanism relies on the same infrastructure as Google Chrome, meaning a small service on your PC checks for new versions every few hours. Once downloaded, the patch installs on the next browser restart. Most users receive updates within 24–48 hours, but you can force the process manually using the steps above.
If you use other Chromium-based browsers, check their respective update channels—this flaw may affect them as well, though patches may not be available yet. Stick to official sources; avoid third-party download sites that could bundle malware.
The bigger picture
The Edge race condition is a stark reminder that even mature software harbors low-level bugs capable of undermining the sandbox model. Browsers are the most-exposed applications on any system, constantly handling untrusted content from the internet. While the CVSS score for CVE-2026-55945 will likely land below 7.0, the real-world impact can spike when chained with other flaws.
For Windows users, Edge’s deep integration into the OS—from PDF rendering to webviews in applications—magnifies the attack surface. Microsoft’s commitment to regular patching is commendable, but the onus remains on users and admins to apply updates without delay.
Looking ahead, a detailed technical write-up from Microsoft’s security team or independent researchers is expected in the coming weeks. In the meantime, staying current with browser updates remains your best defense. The new Edge version also includes performance improvements and other security fixes—details are available in the official release notes.
No action is as simple and effective as checking “About Edge” right now and letting the update do its job. In a world where clicking a link is all it takes to get compromised, keeping your browser engine up to date is non-negotiable.