Google Chrome Hit by Critical ‘Use After Free’ Flaw: CVE-2025-3066 Explained

14 Apr

Why This Chrome Vulnerability Is a Big Deal for Everyone Who Uses the Internet

It’s 2025, and you’d think that our browsers—those sleek portals into the chaotic mess that is the internet—would be ironclad fortresses by now. But no, here we are again. Google Chrome, the browser with more users than any other on Earth, has been hit with yet another critical security flaw. This time it’s a “Use After Free” (UAF) vulnerability, officially tracked as CVE-2025-3066.

And yes, this one’s serious.

What the Hell is a “Use After Free”?

Let’s start with the basics. “Use After Free” vulnerabilities happen when an application continues to access memory after it’s been freed up. Think of it like renting out a flat, moving out, but then still showing up with your key and walking in like you still own the place. Now imagine someone malicious gets your key. That’s what attackers can do with this kind of bug—use and manipulate freed memory, possibly executing arbitrary code.

It’s technical, it’s dangerous, and it’s surprisingly common in complex, fast-moving codebases like web browsers.

Why This One’s Particularly Nasty

What makes CVE-2025-3066 extra spicy is where it lives: Site Isolation. This is Chrome’s big security feature designed to stop one site from snooping on another—especially useful against attacks like Spectre. In theory, Site Isolation keeps each website in its own little box (a separate process), which should mean your online banking session isn’t affected by whatever dodgy tab you forgot to close from last week.

Except… this vulnerability creates an escape hatch. That security sandbox? Potentially compromised. The attacker might be able to run code within Chrome’s process, which could lead to malware installs, credential theft, or just about anything else you don’t want happening on your device.

How It Was Discovered

Security researcher Sven Dysthe reported the flaw on March 21, 2025 and scored a tidy $4,000 from Google’s vulnerability rewards programme. We don’t have the exploit code (thankfully), but Google confirmed that it could lead to heap corruption, which is nerd speak for “we’re in trouble.”

No big exploit campaigns have been spotted in the wild—yet. But don’t get cocky. Vulnerabilities like this tend to surface in exploit kits pretty fast, especially if people are lazy about updates.

Who’s at Risk?

If you're using:

Chrome versions before 135.0.7049.84/.85 on Windows or Mac, or
Chrome versions before 135.0.7049.84 on Linux

…you’re vulnerable.

Yes, that’s almost everyone who hasn’t updated their browser in the last few weeks. And no, Chrome doesn’t always auto-update immediately. That “silent update” feature isn’t quite as silent or fast as we’d like to think.

How to Fix It (Spoiler: It’s Not Hard)

Here’s the fix:

Open Chrome.
Type chrome://settings/help into your address bar.
Let Chrome do its thing. If you see a prompt to restart the browser—do it immediately.

That’s it. If only all cyber defence was this simple, right?

What Makes This Important (Other Than the Obvious)

This isn't just about Chrome. It’s about how fast vulnerabilities can emerge and how slow people are to patch them.

Browser vulnerabilities are some of the most exploitable vectors for attackers. Why? Because browsers:

Interact with untrusted content all day, every day.
Can access things like saved passwords, session cookies, and your webcam/mic.
Are often left open and running for hours, giving attackers more time to do their thing.

Also, let’s not forget this isn’t just about individuals. Organisations that don’t patch browser vulnerabilities are opening themselves up to massive risk. If a user clicks a malicious link in Chrome? Boom—network compromise. If that device is connected to the domain and there's no proper segmentation or privilege management? Boom again—ransomware party.

For IT Teams: Here’s What You Need to Do Today

Enforce browser version checks via MDM or policy.
Deploy endpoint protection that monitors for post-exploitation behaviour (not just file-based malware).
Segment your network. If your finance department is one phishing link away from your production servers, start sweating.
User education still matters. Train people not to click every damn link that says “You’ve won an iPhone.”

And if your MSP isn’t pushing this fix automatically or at least notifying you of the issue? You might want to have a word.

But Wait, There’s More

This update didn’t just fix CVE-2025-3066. It also addressed five other security flaws in Chrome. Google hasn’t shared full details on those yet (standard practice—they wait until most people have updated), but they’ve flagged them as high severity. Which means we’re not just patching one hole—we’re probably fixing a leaking roof.

And the speed of Google's response? Admirable. The flaw was reported in late March, and the patch was pushed by April 8th. That's impressive for a codebase the size of Chrome. Compare that with some vendors who sit on vulns for months before fixing them (cough certain router companies cough).

Final Thoughts

CVE-2025-3066 is a textbook example of why patching matters. It doesn’t matter how many firewalls you have or how many AI-driven endpoint tools you’re paying for—if your software isn’t updated, you’re vulnerable.

This also shows that browser security remains a front line in the war on cyber threats. So if you’re reading this in Chrome, and haven’t checked your version yet, do it now. Don’t be the low-hanging fruit.

Source	Description
NVD	Official CVE tracking from the U.S. National Vulnerability Database.
Cybersecurity News	Initial report and breakdown of CVE-2025-3066.
Google Chrome Release Blog	Google’s official announcement of the fix and Chrome version update.
CVE Details	Expanded technical details and historical context for CVE-2025-3066.
CIS Security Advisory	Mitigation guidance and risk assessment for enterprise environments.
AhnLab Security Blog	Third-party analysis and commentary on the vulnerability’s exploitability.
HKCERT Bulletin	Public cybersecurity advisory for users in Asia-Pacific regions.

Noel Bradford

Noel Bradford – Head of Technology at Equate Group, Professional Bullshit Detector, and Full-Time IT Cynic

As Head of Technology at Equate Group, my job description is technically “keeping the lights on,” but in reality, it’s more like “stopping people from setting their own house on fire.” With over 40 years in tech, I’ve seen every IT horror story imaginable—most of them self-inflicted by people who think cybersecurity is just installing antivirus and praying to Saint Norton.

I specialise in cybersecurity for UK businesses, which usually means explaining the difference between ‘MFA’ and ‘WTF’ to directors who still write their passwords on Post-it notes. On Tuesdays, I also help further education colleges navigate Cyber Essentials certification, a process so unnecessarily painful it makes root canal surgery look fun.

My natural habitat? Server rooms held together with zip ties and misplaced optimism, where every cable run is a “temporary fix” from 2012. My mortal enemies? Unmanaged switches, backups that only exist in someone’s imagination, and users who think clicking “Enable Macros” is just fine because it makes the spreadsheet work.

I’m blunt, sarcastic, and genuinely allergic to bullshit. If you want gentle hand-holding and reassuring corporate waffle, you’re in the wrong place. If you want someone who’ll fix your IT, tell you exactly why it broke, and throw in some unsolicited life advice, I’m your man.

Technology isn’t hard. People make it hard. And they make me drink.

https://noelbradford.com