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BIT-pillow-2026-59204 — Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service

Affected: Bitnami: pillow

Pillow is a Python imaging library. From 8.2.0 through 12.2.0, src/libImaging/Jpeg2KDecode.c accumulates total_component_width across every tile in a JPEG2000 image instead of recomputing it per tile, allowing a crafted tiled JPEG2000 file to force substantially higher transient memory usage and trigger out-of-memory failures during decoding. This issue is fixed in version 12.3.0.

CVE-2026-59204 — Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service

Affected: python-pillow Pillow

GHSA-vjc4-5qp5-m44j — Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service

Affected: PyPI: pillow

### Summary `src/libImaging/Jpeg2KDecode.c:853` accumulates `total_component_width` across every tile in a JPEG2000 image instead of recomputing it per tile. That accumulated value is then used in the `tile_bytes` calculation at `src/libImaging/Jpeg2KDecode.c:868`, which can make the decoder grow `state->buffer` via `realloc` at `src/libImaging/Jpeg2KDecode.c:876` up to roughly one full image's decompressed size even when each tile is small. A crafted tiled JPEG2000 file can therefore force substantially higher transient memory usage and trigger out-of-memory failures during decoding. Based on current evidence, the supported impact is denial of service, not memory corruption.

### Details - Location: `src/libImaging/Jpeg2KDecode.c:853` - Root cause: `total_component_width` is initialized only once before the tile loop and keeps growing across tiles. It is then used to derive `tile_bytes`, so later tiles are treated as if they had the combined component width of all earlier tiles. - Dangerous operation: `tile_bytes` is promoted into `tile_info.data_size`, then `state->buffer` is grown with `realloc` at `src/libImaging/Jpeg2KDecode.c:876`. - Reachability: any attacker-controlled JPEG2000 image with many tiles reaches this path during normal `Image.open(...).load()` decoding.

### PoC The attached helper script and testcase were used: [exercise_j2k_tile_realloc.zip](https://github.com/user-attachments/files/28099912/exercise_j2k_tile_realloc.zip)

Generate the testcase:

```b…

PYSEC-2026-3496 — Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service

Affected: PyPI: pillow

### PoC The attached helper script and testcase were used: [exercise_j2k_tile_realloc.zip](https://github.com/user-attachments/files/28099912/exercise_j2k_tile_realloc.zip)

Generate the testcase:

```b…