GNU Emacs before 31.0.91 contains an integer overflow in the PBM/PPM/PGM image loader that allows an attacker to leak heap memory contents by supplying a crafted image with large dimensions and an elevated max color index. The image loader multiplies image dimensions and channel count using signed integer arithmetic; for sufficiently large values, the result wraps to a negative number, bypassing the bounds check and causing the pixel reader to access heap memory past the end of the allocated buffer. The over-read contents are interpreted as pixel color values and rendered on screen.

GNU Emacs versions before 31.0.91 contain an integer overflow vulnerability in the PBM/PPM/PGM image loader. The flaw arises from signed integer arithmetic used when multiplying image dimensions and channel counts, which can wrap to a negative value for sufficiently large inputs. This negative result bypasses bounds checks, allowing the pixel reader to access heap memory beyond the allocated buffer. An attacker can exploit this by supplying a crafted image with large dimensions and an elevated max color index. The over-read heap memory contents are then interpreted as pixel color values and rendered on screen, effectively leaking sensitive heap data. A fix is available in GNU Emacs 31.0.91.