CAPEC-468: Generic Cross-Browser Cross-Domain Theft
Description
An attacker makes use of Cascading Style Sheets (CSS) injection to steal data cross domain from the victim's browser. The attack works by abusing the standards relating to loading of CSS: 1. Send cookies on any load of CSS (including cross-domain) 2. When parsing returned CSS ignore all data that does not make sense before a valid CSS descriptor is found by the CSS parser.
- Likelihood of attack
- Not rated by MITRE
- Typical severity
- Medium
- Abstraction
- StandardA specific methodology or technique used in an attack.
Mechanism of attack: Inject Unexpected Items
Prerequisites
- No new lines can be present in the injected CSS stringProper HTML or URL escaping of the and ' characters is not presentThe attacker has control of two injection points: pre-string and post-string
Skills required
- HighAbility to craft a CSS injection
Mitigations
- Design: Prior to performing CSS parsing, require the CSS to start with well-formed CSS when it is a cross-domain load and the MIME type is broken. This is a browser level fix.
- Implementation: Perform proper HTML encoding and URL escaping