AGXProbe — CVE-2026-64747 trigger probe

Target: iPhone 13 (A15) on iOS 26.5.2. This app hammers the AGXG14P GPU command-queue paths that plausibly feed a per-queue count bitmask (count >= 0x400 → OOB 0x40-byte slot write → kernel heap corruption).

What we know (reversed, 2026-08-10)

• Vulnerable fn 0xfffffff008003a8c (26.5.2): x1 = 32-bit count mask. For each set bit n it copies a 0x40-byte fixed template (00 00 00 00 + FF×60) into obj+0x1040+n*0x40 and obj+0x1540+n*0x40. 26.6 fix: reject count >= 0x400 (i.e. any bit ≥ 10). Legal slots 0..9.
• The mask is OR-accumulated across a submitted batch from each command's [cmd+0x14] field (wrapper 0xfffffff00800c9d0). The batch slot arrays (10 slots × 0x40) live at object offsets 0x1040 / 0x1540.
• count is not reachable via any static call/literal — the fn is reached through a runtime-built dispatch table (indirect PAC call).
• Unknown: which userland knob feeds [cmd+0x14] (or the mask). That is exactly what this probe tries to discover empirically.

Trigger hypothesis

A submitted batch where some command's 0x14 field (or the OR across the batch) sets a bit ≥ 10. This probe therefore floods every plausible surface with high-bit values: shared-event signal values 1<<k (k=0..31), dense masks (0x3FF|0x400..0xFFFFFFFF), 256-buffer single batches, fences, render + compute + blit, 32 queues.

If the probe triggers the bug, the expected symptoms are, in increasing severity:

1. The app is killed by the system mid-run (userland-side effect of a corrupted queue).
2. The whole device reboots (kernel panic from the OOB heap write hitting a live object). ← strongest signal.
3. Nothing happens (count not controllable through these APIs → need a different trigger surface; report back the log).

Install — prebuilt ipa (CI-built, unsigned)

A ready ipa is built automatically by GitHub Actions on every push and dropped into the build artifacts of the latest run (AGXProbe.ipa). It is unsigned, so install it with any free-Apple-ID sideloader:

• Windows: Sideloadly (or AltStore). Add the ipa, your Apple ID, click Start. The app installs for 7 days.
• macOS: Sideloadly or Xcode (see Build below).

The current ipa: bundle id com.agxprobe.test, arm64, MinOS 17.0. If a sideloader rejects the bundle id, re-sign with a unique id.

Build from source (requires a Mac — any Mac, free Apple ID is fine)

1. Open AGXProbe.xcodeproj in Xcode (16.x).
2. In the project → target AGXProbe → Signing & Capabilities:
   • check Automatically manage signing,
   • select your Team (your free Apple ID / personal team),
   • change PRODUCT_BUNDLE_IDENTIFIER (e.g. com.you.agxprobe1) to anything unique so signing succeeds.
3. Connect the iPhone 13 (iOS 26.5.2), select it as the run destination (Device, not a simulator).
4. Cmd-R. If you get a "preferred signer" / provisioning error, click Enable Development on the device when prompted, then retry.

Run

1. Launch the app. It prints the GPU device name on screen — confirm it shows an A15 GPU (e.g. "Apple A15 GPU") and not a simulator.
2. Press START. Watch the green console log.
3. Phases cycle automatically every 200 iterations: eventStorm → inFlight → fenceStorm → multiQueue → computeHeavy → chainedEvents → mixed → (repeat).
4. Let it run for several minutes. Keep the device awake (disable auto-lock: Settings → Display & Brightness → Auto-Lock → Never).

Reading the result

• Device reboots on its own → the probe tripped the OOB. Now grab the panic log (below) — this both confirms the trigger and gives us the crash site to aim the heap feng shui.
• App killed by system (home screen flashes, "AGXProbe quit") → likely a partial hit; also collect the log.
• Still running after 5+ minutes → count likely not reachable via these exact APIs. Save the on-device log (agxprobe.log in the app's Documents, reachable via Files app because UIFileSharingEnabled is on) and send it back.

Getting the panic log

If it panicked: Settings → Privacy & Security → Analytics & Improvements → Analytics Data → find the newest panic-full-<date> (or JetsamEvent / ipa-log-<timestamp> for a killed app) → Share / AirDrop / copy the tail.

The first lines after "panic(cpu ...)" show the crashing kernel function — send those back.