Severity: High (CVSS 3.1 Base Score: 8.8)
Exploit Status: Actively Exploited in the Wild (Confirmed Zero-Day)
Affected Platforms: Windows, macOS, Linux
Affected Products: Chromium-based browsers, including Microsoft Edge and Google Chrome
1. Executive Overview
CVE-2025-6558 is a high-severity vulnerability affecting the ANGLE (Almost Native Graphics Layer Engine) and GPU process within the Chromium browser engine. Because Microsoft Edge is built directly on Chromium, it is equally affected.
The flaw results from insufficient validation of untrusted input during the handling of WebGL and graphics instructions. Under specific conditions, this allows a remote attacker to escape the browser sandbox and execute arbitrary code on the host system with the same privileges as the logged-in user.
This vulnerability was discovered during investigations of real-world attacks and was actively exploited prior to patch availability, classifying it as a true zero-day.
2. Vulnerability Classification
- Vulnerability Name: Insufficient Validation of Untrusted Input in ANGLE
- Attack Vector: Network (malicious website)
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: Required (visiting a malicious page)
- Scope: Unchanged
- Impact:
- Confidentiality: High
- Integrity: High
- Availability: High
CVSS Vector:CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
3. Why ANGLE Matters (Architecture Context)
Modern browsers do not allow web pages to interact directly with the graphics hardware. Instead, they use ANGLE as an intermediary layer.
The graphics pipeline works as follows:
- Web Page Input: A website sends high-level WebGL instructions through JavaScript.
- ANGLE Translation: ANGLE converts those instructions into low-level DirectX, Vulkan, or OpenGL commands.
- GPU Execution: The GPU driver executes those commands to render graphics.
ANGLE exists to ensure performance and security. CVE-2025-6558 breaks that security assumption.
4. Root Cause of the Vulnerability
The core issue lies in a missing or incomplete validation check inside ANGLE’s handling of certain graphics data structures.
Specifically:
- The browser accepts malformed or oversized WebGL input from a web page.
- ANGLE fails to properly verify buffer sizes, memory bounds, or integer values before translating that input.
- Invalid data is passed to the GPU process unchecked.
This leads directly to memory corruption in a privileged browser process.
5. Step-by-Step Exploit Chain
Step 1: Crafting the Malicious Page
The attacker creates a webpage that uses WebGL to submit deliberately malformed graphics instructions. These instructions may include:
- Oversized buffers
- Invalid shader parameters
- Corrupted geometry or texture metadata
JavaScript is used to repeatedly invoke WebGL functions such as gl.bufferData() or gl.drawArrays() to reliably trigger the flaw.
Step 2: Validation Failure in ANGLE
When the victim loads the page:
- The browser renderer forwards the WebGL commands to ANGLE.
- ANGLE fails to fully sanitize the input.
- Malicious data is translated into low-level GPU commands without proper safety checks.
This is the critical failure point.
Step 3: Memory Corruption in the GPU Process
The corrupted instructions reach the GPU process, which runs outside the strict web content sandbox.
As a result:
- The GPU process performs out-of-bounds reads or writes.
- Heap memory becomes corrupted.
- Attackers may use heap spraying techniques to make memory layout predictable.
Step 4: Sandbox Escape
The GPU process has more system access than the renderer sandbox.
By corrupting control data in memory, the attacker:
- Overwrites function pointers or return addresses
- Redirects execution flow to attacker-controlled shellcode
- Gains code execution inside the GPU process
At this point, the browser sandbox is effectively bypassed.
Step 5: Remote Code Execution
Once code execution is achieved:
- The attacker can run arbitrary commands as the current user
- Additional malware can be downloaded and executed
- Persistence mechanisms may be installed
- Sensitive data can be accessed or exfiltrated
No further browser vulnerabilities are required.
6. Real-World Impact
Successful exploitation of CVE-2025-6558 can result in:
- Full compromise of the user session
- Theft of credentials, cookies, and local files
- Installation of spyware, ransomware, or backdoors
- System instability or crashes due to GPU process failure
Because exploitation requires only a website visit, this vulnerability is particularly dangerous in phishing or drive-by attack scenarios.
7. Patch and Remediation
Official Fixed Versions
Microsoft Edge
- Fixed in: Version 138.0.3351.95 and later
Google Chrome
- Fixed in: Version 138.0.7204.157 / 138.0.7204.158 and later
Official Patch Pages
Microsoft Edge Security Updates:
https://learn.microsoft.com/en-us/deployedge/microsoft-edge-relnotes-security
Chrome Stable Channel Updates:
https://chromereleases.googleblog.com
8. Recommended Actions
For End Users
- Update the browser immediately to a patched version.
- Restart the browser to ensure the update is applied.
- Avoid visiting untrusted or unknown websites until fully patched.
For Enterprise & Security Teams
- Treat this as a priority emergency patch.
- Enforce browser version compliance across all endpoints.
- Monitor for abnormal GPU process crashes or browser instability.
- Review web proxy and endpoint telemetry for signs of exploitation attempts.
9. Mitigation Notes
There is no reliable configuration-only mitigation for this vulnerability.
- Disabling WebGL may reduce exposure but will break many legitimate applications.
- Antivirus alone cannot reliably block this exploit chain.
- Applying the vendor patch is the only effective defense.
10. Summary
CVE-2025-6558 represents a serious failure in graphics input validation that allows attackers to move from a malicious webpage to full system compromise. Its exploitation in the wild, low attack complexity, and sandbox escape capability make it one of the more dangerous browser vulnerabilities observed in 2025.
If your browser is not on version 138 or later, it should be considered vulnerable.
