Pillow CVE-2026-42308

Pillow is a Python Imaging Library that processes fonts and renders text. When rendering glyphs from a TrueType or OpenType font, the library tracks the current horizontal position by accumulating the advance width of each glyph. The vulnerability exists in this position-tracking logic: if a single glyph's advance value is extremely large (close to or exceeding the maximum value of a signed integer), adding it to the current position causes an integer overflow. On systems using 32-bit integers, this overflow wraps the position to a negative or small positive value, corrupting subsequent memory writes or reads during glyph rendering. The root cause is improper input validation and lack of bounds checking before arithmetic operations on font metrics (CWE-190: Integer Overflow or Wraparound).