ImageMagick: Stack buffer overflow in FTXT reader via oversized integer field

Summary

A stack-based buffer overflow exists in the ImageMagick FTXT image reader. A crafted FTXT file can cause out-of-bounds writes on the stack, leading to a crash.

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==3537074==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffee4850ef0 at pc 0x5607c408fb33 bp 0x7ffee484fe50 sp 0x7ffee484fe40
WRITE of size 1 at 0x7ffee4850ef0 thread T0