A zero-width PPM image crashes Pillow's morphology code

Pillow: Out-of-bounds access in _imagingmorph on a zero-width image

Advisory

CVE-2026-112397

Library

Pillow, pillow on PyPI

Published

2026-10-19

Severity

not scored upstream

Affected

< 12.3.0

Fixed in

12.3.0

Reaches you

through another call

What triggers it

Image.open on a PPM or PGM file declaring a width of 0, then ImageMorph.MorphOp.apply on it.

What sillybos does

Refused by default

sillybos refuses the triggering file under its default policy, through the format check.

A PPM file is not one of the four formats a scan can be and is refused as an unknown format; a zero dimension is refused in the formats sillybos does read. The crash itself is in a morphology call opening a file never makes.

Proposed from the advisory's text on 2026-11-01, as part of folding the backfill into the record; confirmed by a person on 2026-11-03.

Proved by these tests in the sillybos suite, each of which builds the triggering file from bytes and checks that it is refused:

• tests/test_check.py::TestHostileFiles::test_an_unknown_format
• tests/test_check.py::TestHostileFiles::test_an_image_with_a_zero_dimension

How to protect yourself

In general. Upgrade to Pillow 12.3.0.

Specifically. Open with formats limited to the readers you mean to use, as open_checked does.

The general advice applies to every row here.

Sources

• https://osv.dev/vulnerability/GHSA-58r4-6rv3-gfh8
• https://osv.dev/vulnerability/PYSEC-2026-4329
• The record entry, triaged 2026-11-03, last checked 2026-11-03