PoC for an integer overflow vulnerability in ImageIO patched in iOS/macOS 26.5 (CVE-2026-28990)

Bug discovered by Jiri Ha & Arni Hardarson

There was an integer overflow in function EXRReadPlugin::decodeBlockAppleEXR prior to iOS/macOS 26.5 when calculating the size of a buffer.

It is possible to cause memory corruption by having the multiplication of the supplied image's width and height values wrap-around to 0, and subsequently call malloc_type_malloc with a very small size.

Supplying an image file containing excess pixel data results in a heap overflow and a crash:

  thread #5, queue = 'com.apple.root.user-interactive-qos', stop reason = EXC_GUARD (code=1, subcode=0x4141414141414151)
    frame #0: 0x00000001855ba8c8 libdispatch.dylib`_dispatch_root_queue_drain + 176
libdispatch.dylib`_dispatch_root_queue_drain:
->  0x1855ba8c8 <+176>: ldr    x8, [x0, #0x10]!
    0x1855ba8cc <+180>: cbz    x8, 0x1855bab2c ; <+788>
    0x1855ba8d0 <+184>: str    x8, [x20, #0x68]
    0x1855ba8d4 <+188>: mov    x0, x20
Target 0: (exr_parser) stopped.

Full technical write-up available here Video explanation available here