Cross-site Scripting (XSS) possible due to improper sanitisation of `href` attributes on `<a>` tags

Summary

There is a potential cross-site scripting (XSS) vulnerability that can be exploited via maliciously crafted user data.

Our filter to detect and prevent the use of the javascript: URL scheme in the href attribute of an <a> tag could be bypassed with tab \t or newline \n characters between the characters of the protocol, e.g. java\tscript:.

Impact

If you render an <a> tag with an href attribute set to a user-provided link, that link could potentially execute JavaScript when clicked by another user.

a(href: user_profile) { "Profile" }

Mitigation

The best way to mitigate this vulnerability is to update to one of the following versions:

• 1.10.1
• 1.9.2
• 1.8.3
• 1.7.2
• 1.6.3
• 1.5.3
• 1.4.2

Workarounds

Configuring a Content Security Policy that does not allow unsafe-inline would effectively prevent this vulnerability from being exploited.