Python-Pillow

A vulnerability in Pillow's `PcfFontFile._load_bitmaps()` function allows for a decompression bomb check bypass when loading PCF fonts. Attacker-controlled glyph dimensions from the PCF `METRICS` section are passed directly to `Image.frombytes()` without validation, leading to excessive memory allocation. This can be exploited to cause denial of service (resource exhaustion) through either persistent attacks by providing matching bitmap data or transient attacks by providing a small PCF file with large declared dimensions, leading to a large C-heap buffer allocation before an exception. Systems loading PCF fonts from untrusted sources are at risk.