FAQ-000303 - CSS and UI Security / Improper CSS Loading Vulnerabilities

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Current FAQ

Question
What does "CSS Outside Component" vulnerability mean and how do I fix it?
Answer
A "CSS Outside Component" vulnerability occurs when CSS directives are used in a way that violates style isolation principles. This can lead to namespace isolation breaches, where one component's CSS unintentionally affects the functionality or appearance of another component. For example, using absolute or fixed positioning in CSS can cause such issues if the component is exposed outside its namespace. ### Standard Fix: 1. **Use Relative Positioning**: Prefer relative positioning over absolute or fixed positioning unless the component is strictly confined to its namespace. 2. **Avoid Risky CSS Directives**: Refrain from using CSS properties that could compromise the isolation of components. 3. **Design for Isolation**: Ensure components are securely designed to function within their namespace without interfering with others. ### Addressing CSS Outside Component Issues in Security Review: 1. **Adhere to Style Isolation**: Avoid using CSS directives that conflict with style isolation, such as absolute positioning, unless the component is not globally exposed. If the `isExposed` attribute is set to `true`, use relative positioning to reduce risks. 2. **Use Static Resources for Third-Party CSS**: Save third-party CSS files in static resources and reference them securely using the `<ltng:require>` tag in your component markup. 3. **Prevent Namespace Breaches**: Ensure your CSS does not interfere with other components by maintaining strict namespace isolation. 4. **Follow Secure Coding Practices**: Align your solution with Salesforce's security policies and guidelines, as outlined in the Salesforce Packaging Guide. ### Best Practices: - Maintain secure and isolated component behavior - Ensure CSS doesn't breach namespace boundaries - Use appropriate positioning methods based on component exposure - Follow Salesforce's security documentation and guidelines Following these practices helps maintain secure and isolated component behavior and ensures your components pass the security review without issues.

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Related Security Rules (click to view)
LoadCSSApexStylesheetLoadCSSLinkHref
Question
What does "CSS Outside Component" vulnerability mean and how do I fix it?
Recommended Answer Update
A "CSS Outside Component" vulnerability occurs when CSS directives are used in a way that violates style isolation principles. This can lead to namespace isolation breaches, where one component's CSS unintentionally affects the functionality or appearance of another component. For example, using absolute or fixed positioning in CSS can cause such issues if the component is exposed outside its namespace. ### Standard Fix: 1. **Use Relative Positioning**: Prefer relative positioning over absolute or fixed positioning unless the component is strictly confined to its namespace. 2. **Avoid Risky CSS Directives**: Refrain from using CSS properties that could compromise the isolation of components. 3. **Design for Isolation**: Ensure components are securely designed to function within their namespace without interfering with others. ### Addressing CSS Outside Component Issues in Security Review: 1. **Adhere to Style Isolation**: Avoid using CSS directives that conflict with style isolation, such as absolute positioning, unless the component isn't globally exposed. If the `isExposed` attribute is set to `true`, use relative positioning to reduce risks. 2. **Use Static Resources for Third-Party CSS**: Save third-party CSS files in static resources and reference them securely using the `<ltng:require>` tag in your component markup. 3. **Prevent Namespace Breaches**: Ensure your CSS doesn't interfere with other components by maintaining strict namespace isolation. 4. **Follow Secure Coding Practices**: Align your solution with Salesforce's security policies and guidelines, as outlined in the Salesforce Packaging Guide. ### Best Practices: - Maintain secure and isolated component behavior - Ensure CSS doesn't breach namespace boundaries - Use appropriate positioning methods based on component exposure - Follow Salesforce's security documentation and guidelines Following these practices helps maintain secure and isolated component behavior and ensures your components pass the security review without issues.
Reasoning
I made minimal language improvements for clarity: changed 'is not globally exposed' to 'isn't globally exposed' for a more conversational tone per the FAQ guidelines. The content is accurate and comprehensive. I associated this FAQ with LoadCSSApexStylesheet and LoadCSSLinkHref rules because both directly relate to CSS loading vulnerabilities that the FAQ addresses. LoadCSSApexStylesheet detects when CSS is loaded through apex:stylesheet tags which can cause namespace isolation issues - this matches the FAQ's discussion of CSS directives violating style isolation principles and causing namespace breaches. LoadCSSLinkHref identifies CSS loaded through link href attributes which can also compromise component isolation - this aligns with the FAQ's guidance on using static resources and proper CSS loading techniques to maintain namespace boundaries. The FAQ's core teaching about preventing CSS from affecting other components outside their namespace directly corresponds to what these security rules are designed to detect and prevent.
Reasoning References