Silverware Games is a social network where people can play games online. Users can attach URLs to YouTube videos, the site will generate related <iframe> when the post will be published. The handler has some sort of protection so non-YouTube links cant be posted, as well as HTML tags are being stripped. However, it was still possible to add custom HTML attributes (e.g. onclick=alert(xss)) to the <iframe>. This issue was fixed in the version 1.1.34` and does not require any extra actions from our members. There has been no evidence that this vulnerability was used by anyone at this time.
Weakness
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as “<”, “>”, and “&” that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Silverwaregames |
Silverwaregames |
* |
1.1.34 (excluding) |
Potential Mitigations
- Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
- The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
References