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CAPEC-468: Generic Cross-Browser Cross-Domain Theft

Attack Pattern ID: 468
Abstraction: Standard
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+ 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.
+ Extended Description

By having control of some text in the victim's domain, the attacker is able to inject a seemingly valid CSS string. It does not matter if this CSS string is preceded by other data. The CSS parser will still locate the CSS string. If the attacker is able to control two injection points, one before the cross domain data that the attacker is interested in receiving and the other one after, the attacker can use this attack to steal all of the data in between these two CSS injection points when referencing the injected CSS while performing rendering on the site that the attacker controls. When rendering, the CSS parser will detect the valid CSS string to parse and ignore the data that "does not make sense". That data will simply be rendered. That data is in fact the data that the attacker just stole cross domain. The stolen data may contain sensitive information, such CSRF protection tokens.

+ Typical Severity


+ Relationships
Section HelpThis table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
ChildOfMeta Attack PatternMeta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.242Code Injection
Section HelpThis table shows the views that this attack pattern belongs to and top level categories within that view.
+ 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
[Level: High]
Ability to craft a CSS injection
+ Resources Required
Attacker controlled site/page to render a page referencing the injected CSS string
+ 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
+ References
[REF-405] Chris Evans. "Generic cross-browser cross-domain theft". 2009-12-28. <>.
+ Content History
Submission DateSubmitterOrganization
(Version 2.6)
CAPEC Content TeamThe MITRE Corporation
Modification DateModifierOrganization
(Version 2.7)
CAPEC Content TeamThe MITRE Corporation
Updated Related_Attack_Patterns
(Version 2.8)
CAPEC Content TeamThe MITRE Corporation
Updated Related_Attack_Patterns
(Version 3.4)
CAPEC Content TeamThe MITRE Corporation
Updated Mitigations
(Version 3.7)
CAPEC Content TeamThe MITRE Corporation
Updated Description, Extended_Description
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Page Last Updated or Reviewed: July 31, 2018