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BIT-pillow-2026-55798 — Pillow: WindowsViewer.get_command() OS command injection via unescaped shell path

Affected: Bitnami: pillow

Pillow is a Python imaging library. Prior to 12.3.0, WindowsViewer.get_command() constructed a cmd.exe shell command by directly embedding a file path into an f-string without escaping and passed the result to subprocess.Popen(..., shell=True), allowing shell metacharacters in the file path to inject arbitrary cmd.exe commands. This issue is fixed in version 12.3.0.

CVE-2026-55798 — Pillow: WindowsViewer.get_command() OS command injection via unescaped shell path

Affected: python-pillow Pillow

GHSA-4x4j-2g7c-83w6 — Pillow: WindowsViewer.get_command() OS command injection via unescaped shell path

Affected: PyPI: Pillow

### 1. Summary

`WindowsViewer.get_command()` constructs a `cmd.exe` shell command by directly embedding a file path into an f-string without escaping. The result is passed to `subprocess.Popen(..., shell=True)`. Shell metacharacters in the file path — most importantly a double-quote (`"`) that breaks out of the wrapping, followed by `&` — allow injection of arbitrary `cmd.exe` commands.

The macOS equivalent (`MacViewer`) correctly applies `shlex.quote()` to the same parameter. The Linux equivalent (`UnixViewer`) does likewise. Windows is the only platform missing this protection, despite `shlex.quote` being **already imported** on line 21 of `ImageShow.py`.

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### 2. Vulnerable Code

**File:** `src/PIL/ImageShow.py`, lines 133–150

```python class WindowsViewer(Viewer): format = "PNG" options = {"compress_level": 1, "save_all": True}

def get_command(self, file: str, **options: Any) -> str: return ( f'start "Pillow" /WAIT "{file}" ' # ← f-string, no escaping "&& ping -n 4 127.0.0.1 >NUL " f'&& del /f "{file}"' # ← same path, unescaped again )

def show_file(self, path: str, **options: Any) -> int: if not os.path.exists(path): raise FileNotFoundError subprocess.Popen( self.get_command(path, **options), shell=True, # ← shell=True creationflags=getattr(subprocess, "CREATE_NO_WINDOW"), ) # nos…

PYSEC-2026-2257

Affected: PyPI: pillow