Affected: Homebrew: aider

``` ============================================================================ ReDoS in XbmImagePlugin: 512-byte file stalls Image.open() for minutes Location: src/PIL/XbmImagePlugin.py:58 in XbmImageFile._open() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ```

A crafted 512-byte file makes Pillow's `Image.open()` spend about six minutes of processor time on one core before it gives up with `UnidentifiedImageError`. Anyone who can hand bytes to an application that opens images with Pillow's default settings can trigger this, for example through an upload form, a thumbnailer, or a service that checks whether a blob is an image. A few such files sent at once can tie up a typical pool of worker processes.

The cause is the `xbm_head` regular expression in `src/PIL/XbmImagePlugin.py:32-40`, which `XbmImageFile._open()` (line 58) runs over the first 512 bytes of any stream whose prefix starts with `#define`. Several adjacent parts of the pattern can match the same characters. `[ \t]+` overlaps with `.*` in the width and height lines and with `[^_]*` in the optional hotspot lines, and `[\r\n]+` closing the hotspot group overlaps with the following `[\000-\377]*`. The header sets a run of k spaces after each `#define` and a run of k line terminators after `_y_hot`, then omits the `[]` after `_bits`. That forces Python's backtracking matcher to try every way of splitting those runs and rescan the…

Pillow is a Python imaging library. Prior to 13.0.0, Pillow's XBM header parser is vulnerable to regular-expression denial of service. In XbmImageFile._open, when an application calls Image.open() on a small crafted XBM file, XbmImagePlugin applies a backtracking expression to the attacker-controlled header before image dimensions are accepted, stalling a worker for minutes and denying service. This issue is fixed in version 13.0.0.

Affected: PyPI: Pillow

``` ============================================================================ ReDoS in XbmImagePlugin: 512-byte file stalls Image.open() for minutes Location: src/PIL/XbmImagePlugin.py:58 in XbmImageFile._open() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ```

A crafted 512-byte file makes Pillow's `Image.open()` spend about six minutes of processor time on one core before it gives up with `UnidentifiedImageError`. Anyone who can hand bytes to an application that opens images with Pillow's default settings can trigger this, for example through an upload form, a thumbnailer, or a service that checks whether a blob is an image. A few such files sent at once can tie up a typical pool of worker processes.

The cause is the `xbm_head` regular expression in `src/PIL/XbmImagePlugin.py:32-40`, which `XbmImageFile._open()` (line 58) runs over the first 512 bytes of any stream whose prefix starts with `#define`. Several adjacent parts of the pattern can match the same characters. `[ \t]+` overlaps with `.*` in the width and height lines and with `[^_]*` in the optional hotspot lines, and `[\r\n]+` closing the hotspot group overlaps with the following `[\000-\377]*`. The header sets a run of k spaces after each `#define` and a run of k line terminators after `_y_hot`, then omits the `[]` after `_bits`. That forces Python's backtracking matcher to try every way of splitting those runs and rescan the…

Affected: Ubuntu:Pro:14.04:LTS: pillow, Ubuntu:Pro:16.04:LTS: pillow, Ubuntu:Pro:18.04:LTS: pillow, Ubuntu:Pro:20.04:LTS: pillow, Ubuntu:Pro:20.04:LTS: pillow-python2, Ubuntu:22.04:LTS: pillow, Ubuntu:24.04:LTS: pillow, Ubuntu:26.10: pillow, Ubuntu:26.04:LTS: pillow

(Pillow is a Python imaging library. Prior to 13.0.0, Pillow's XBM head ...)