GHSA-vpxv-r9pg-7gpr

The UIL and XPM image encoder do not validate the pixel index value returned by `GetPixelIndex()` before using it as an array subscript. In HDRI builds, `Quantum` is a floating-point type, so pixel index values can be negative. An attacker can craft an image with negative pixel index values to trigger a global buffer overflow read during conversion, leading to information disclosure or a process crash.

``` READ of size 1 at 0x55a8823a776e thread T0 #0 0x55a880d01e85 in WriteUILImage coders/uil.c:355 ```

``` READ of size 1 at 0x55fa1c04c66e thread T0 #0 0x55fa1a9ee415 in WriteXPMImage coders/xpm.c:1135 ```