A negative byte count in an EPS file loops Image.open for ever

Pillow EpsImagePlugin negative %%BeginBinary byte count causes infinite loop denial of service

Advisory

CVE-2026-59203

Library

Pillow, pillow on PyPI

Published

2026-07-14

Severity

5.3 out of 10, as published

Affected

>= 12.0.0, <= 12.2.0

Fixed in

12.3.0

Reaches you

by opening a file

What triggers it

Image.open on an EPS file whose %%BeginBinary directive carries a negative byte count; the loop is in Image.open itself, before any load.

What sillybos does

Refused by default

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

A PostScript file is refused by name before Pillow sees it: the first bytes say what it is, whatever its name. This is the EPS reader October's command-execution flaw was also in.

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 this test in the sillybos suite, which builds the triggering file from bytes and checks that it is refused:

• tests/test_check.py::TestHostileFiles::test_a_renamed_postscript_file

How to protect yourself

In general. Upgrade to Pillow 12.3.0.

Specifically. Refuse PostScript by name, as sillybos does by default, and never hand Pillow an EPS from outside.

The general advice applies to every row here.

Sources

• https://osv.dev/vulnerability/GHSA-pg7v-jwj7-p798
• https://osv.dev/vulnerability/PYSEC-2026-3452
• The record entry, triaged 2026-11-03, last checked 2026-11-03