Sanitize SVGs in WordPress

So my plugin Safe SVG has just been accepted into the WordPress plugin directory. Whilst mainly a proof of concept, I’m hoping that this plugin will help convince the core team that SVGs, with the right sanitization should become part of core.

My major argument for allowing SVGs in core with sanitization is that there are currently 128 other SVG upload plugins in the plugin directory (source), plus the likes of the posts on blogs like CSS Tricks such as this one that all show you how to allow SVG uploads in WordPress, but don’t address or sometimes even mention the massive security risks that come with allowing users to upload SVGs.

SVGs should be considered as standalone XML applications, there are a huge number of vulnerabilities that can be attacked. For example, some of the easiest to implement are XXE attacks and the Billion Laughs attack. Safe SVG nullifies these attacks by removing the DOCTYPE from the SVG file, something so simple yet overlooked by most other plugins.

Safe SVG also protects against XSS attacks embedded within the XML file by defining a strict whitelist of elements and attributes allowed within the SVG, anything not on these whitelists are removed. Whilst this may break some Javascript powered SVG animations, I feel that is a small price to pay for peace of mind when it comes to your users security.

Probably the best way to learn more about Safe SVG is to go and download it from the WordPress plugin directory and take a look through the code, alternatively you can see the library it’s built upon on Github. If you find a bypass or have any suggestions on how to improve this plugin or the underlying library, please don’t hesitate to contact me and let me know your thoughts.

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