mojo_debug --interface content.mojom.FrameHost --exploit cve-2025-48543
Executive Summary: The Perimeter is Not the Prison
In modern browser security, the "Renderer" process—the part that actually parses and draws webpages—is heavily sandboxed. Even if an attacker achieves Remote Code Execution (RCE) via a vulnerability like WebKit's CVE-2025-43529, they are trapped. They cannot access the filesystem, the microphone, or sensitive system APIs.
To truly compromise a device, the attacker must find a "Sandbox Escape."
CVE-2025-48543 is a critical Use-After-Free (UAF) vulnerability within Chrome's Mojo IPC framework. By exploiting a race condition in how Mojo handles cross-process message pipes, a compromised renderer process can corrupt memory in the high-privilege browser process. This provides the ultimate "get out of jail free" card: arbitrary code execution with the full privileges of the Chrome application.
Technical Architecture: Mojo IPC and the Broker Model
Chrome follows a multi-process architecture. The Browser Process acts as the broker, managing all system-level resources. The Renderer Processes are the low-privilege workers.
The Mojo Framework
Mojo is the connective tissue. It uses "Message Pipes" to send asynchronous messages between processes. Each pipe has two "Handles."
- One handle is held by the Renderer.
- One handle is held by the Browser.
When a Renderer wants to open a file or access the network, it sends a request over a Mojo handle to a specific interface (like `content.mojom.FrameHost`) in the Browser process.
Handle Management
The Browser process maintains a global map of all active Mojo handles. When a handle is closed in one process, the Mojo daemon must ensure that all references to that handle are invalidated across all other processes.
Vulnerability Root Cause: The Handle Re-entry Race
The root cause of CVE-2025-48543 is a Use-After-Free in the Browser process's `MojoHandleManager`.
The Race Condition
The vulnerability is triggered during a complex sequence of rapid handle creation and destruction:
- The renderer creates a large number of message pipes.
- The renderer sends a message to the browser process to close a specific handle.
- Simultaneously, the renderer sends another message that relies on that same handle being "transferred" to a new interface.
The Use-After-Free
Due to a logic error in the browser process's task scheduler, the "close" operation and the "transfer" operation can be processed out of order or in a re-entrant manner.
The `MojoHandleManager` frees the handle object in response to the first message but fails to remove it from a temporary "pending transfer" list. When the second message is processed, the manager attempts to access the handle object from the pending list—but the memory has already been freed.
Exploitation Methodology: Escaping the Sandbox
Triggering the UAF from the Compromised Renderer
Assuming the attacker already has RCE in the renderer, they can use JavaScript (via Mojo bindings) to trigger the race condition.
// Triggering Mojo UAF
let pipe = Mojo.createMessagePipe();
let handle0 = pipe.handle0;
let handle1 = pipe.handle1;
// Rapid close and transfer
handle0.close();
// This call in the browser process will use the freed handle0
content.mojom.FrameHost.getRemote().passHandle(handle0); Browser Process Heap Grooming
To weaponize the UAF, the attacker must replace the freed handle object in the browser process with data they control. They do this by "spraying" the browser process's heap with other Mojo messages or blob data.
The goal is to overwrite the vtable pointer of the freed handle object with a pointer to an attacker-controlled ROP chain.
Achieving Escape
When the Browser process's `MojoHandleManager` attempts to call a method (like `OnMessageReceived`) on the corrupted handle, it instead executes the attacker's ROP chain. The attacker has now escaped the renderer's sandbox and can execute arbitrary code with the privileges of the Chrome app, allowing them to access the camera, location, and stored cookies.
Remediation and Mitigation
The Technical Fix
The fix implemented in Chrome 145.0+ involved a complete rewrite of the `MojoHandleManager` task synchronization. The manager now uses "Strong Pointers" (`scoped_refptr`) for all handle objects during the transfer phase, ensuring that a handle cannot be freed as long as it exists in any pending list.
Defensive Posture
- Update Chrome: Ensure you are running the latest version of Chrome (or the Android System WebView).
- Site Isolation: Chrome's Site Isolation feature helps by placing different websites in different processes, but it does not protect against a full sandbox escape once a process is compromised.
- Hardware-Backed Sandboxing: Newer Android versions utilize hardware-assisted virtualization (pKVM) to further isolate sensitive components, making even a Mojo-level escape significantly more difficult to leverage for full system compromise.