CVE-2023-36828

Description

Antlers sanitizer cannot effectively sanitize malicious SVG ### Summary The SVG tag does not sanitize malicious SVG. Therefore, an attacker can exploit this vulnerability to perform XSS attacks using SVG, even when using the `sanitize` function. ### Details Regarding the previous discussion mentioned [here](https://github.com/statamic/cms/security/advisories/GHSA-jvw9-rrc5-39g6#advisory-comment-84322), it has been identified that the default blacklist in the **FilesFieldtypeController** (located at this [link](https://github.com/statamic/cms/blob/f806b6b007ddcf066082eef175653c5beaa96d60/src/Http/Controllers/CP/Fieldtypes/FilesFieldtypeController.php#L15)) only blocks certain file extensions such as php, php3, php4, php5, and phtml. This allows a malicious user to upload a manipulated SVG file disguised as a social media icon, potentially triggering an XSS vulnerability. ### PoC Screenshot  ### PoC 1. Create new Global set, let's say "Settings" 2. Create a "Grid" field in Blueprint (named: social), then add somefields Name (text), URL (text) and Icon (Assets) in the section Fields. 3. When calling the social setting in the `_footer.antlers.html`, remember to [sanitize](https://statamic.dev/modifiers/sanitize) ``` {{ settings:social }} <a href="{{ $url }}" class="ml-4" aria-label="{{ $name }}" rel="noopener"> {{ svg :src="icon" class="h-6 w-6 hover:text-hot-pink" | sanitize }} </a> {{ /settings:social }} ``` 4. Upload the malicious SVG image, here is the code: ``` <?xml version="1.0" standalone="no"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> <svg width="500" height="500" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> <text x="20" y="35">Statamic</text> <foreignObject width="500" height="500"> <iframe xmlns="http://www.w3.org/1999/xhtml" src="javascript:confirm(document.cookie);" width="400" height="250"/> </foreignObject> </svg> ``` ### Impact Since the social media icon is displayed in the footer layout, any user can view it, potentially leading to the execution of XSS. ### Suggestions to Mitigate or Resolve the Issue: Sanitize when outputing the svg. This vulnerability caused by unsanitized `File::get()` when retrieving the SVG, it is crucial to sanitize the SVG when outputting it. The issue can be found in the following file: https://github.com/statamic/cms/blob/f806b6b007ddcf066082eef175653c5beaa96d60/src/Tags/Svg.php#L36-L40. It is highly recommended to implement proper sanitization measures to ensure the security of the SVG content. One effective approach is to utilize a reliable package, such as https://github.com/darylldoyle/svg-sanitizer ,which provides comprehensive SVG sanitization capabilities. So the code becomes: ```php use enshrined\svgSanitize\Sanitizer; if (File::exists($file)) { $sanitizer = new Sanitizer(); $dirtySVG = File::get($file); $svg = $sanitizer->sanitize($dirtySVG); break; } ``` ### Reference - https://github.com/gogs/gogs/security/advisories/GHSA-ff28-f46g-r9g8 - https://huntr.dev/bounties/34a12146-3a5d-4efc-a0f8-7a3ae04b198d/ - https://blog.nintechnet.com/wordpress-elementor-plugin-fixed-svg-xss-protection-bypass-vulnerability/