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BIT-pillow-2026-54059 — Pillow: PcfFontFile._load_bitmaps()`: `Image.frombytes()` called without `_decompression_bomb_check()` — bomb protectio…

2026-09-30T21:11:54.894191+00:00

Affected: Bitnami: pillow

Pillow is a Python imaging library. Prior to 12.3.0, PIL/PcfFontFile.py _load_bitmaps() read glyph dimensions from the PCF METRICS section and passed them directly to Image.frombytes() without calling Image._decompression_bomb_check(), allowing crafted PCF font data to cause excessive memory allocation. This issue is fixed in version 12.3.0.

CVE-2026-54059 — Pillow: PcfFontFile._load_bitmaps()`: `Image.frombytes()` called without `_decompression_bomb_check()` — bomb protectio…

2026-09-30T21:11:54.894312+00:00

Affected: python-pillow Pillow

GHSA-8v84-f9pq-wr9x — Pillow `PcfFontFile._load_bitmaps()`: `Image.frombytes()` called without `_decompression_bomb_check()` — bomb protectio…

2026-09-30T21:11:54.894373+00:00

Affected: PyPI: pillow

## Description `PIL/PcfFontFile.py` `_load_bitmaps()` (line 227) reads glyph dimensions from the PCF `METRICS` section and passes them directly to `Image.frombytes()` without calling `Image._decompression_bomb_check()`. Dimensions originate from unsigned 16-bit values:

``` xsize = right - left (max: 65535 − 0 = 65535) ysize = ascent + descent (max: 65535 + 65535 = 131070) ```

Maximum exploitable pixel count: **65,535 × 131,070 = 8,589,734,450 pixels** — **48× the DecompressionBombError threshold**.

**Vulnerable code (`PIL/PcfFontFile.py` line 224–227):** ```python for i in range(nbitmaps): xsize, ysize = metrics[i][:2] # from PCF METRICS — attacker-controlled b, e = offsets[i : i + 2] bitmaps.append( Image.frombytes("1", (xsize, ysize), data[b:e], "raw", mode, pad(xsize)) # ↑ NO _decompression_bomb_check()! ) ```

`Image.frombytes()` calls `Image.new()` first (allocating the full C-heap buffer), **then** attempts to fill it. This creates two distinct attack paths:

- **Persistent attack**: Provide matching bitmap data → `frombytes()` succeeds → image stored in `font.glyph[ch]` permanently - **Transient attack**: Provide a 148-byte PCF file with large declared dimensions but no data → `Image.new()` allocates the full buffer → `ValueError` → buffer freed → but the spike occurs before Python can respond

## Steps to reproduce

**Proof of Concept script:**

```python #!/usr/bin/env python3 """PoC: PcfFontFile bomb bypass — 148-…

PYSEC-2026-2253

2026-09-30T21:11:54.894503+00:00

Affected: PyPI: pillow