Skip to content

Latest commit

 

History

History
49 lines (42 loc) · 6.92 KB

threat-modeling.md

File metadata and controls

49 lines (42 loc) · 6.92 KB

Threat Model Analysis for kkuchta/css-only-chat

Threat: CSS Injection into Message Display

  • Description: An attacker injects malicious CSS through a vulnerability in how the application integrates with css-only-chat. Because the library relies heavily on CSS for rendering message content and styling, injected CSS can directly manipulate the appearance of messages. The attacker could alter the sender's name, visually modify the message content, or insert deceptive elements (like fake links) by targeting the library's CSS classes and structure. This is a direct threat because the library's core design makes it inherently vulnerable to CSS manipulation.
    • Impact:
      • Impersonation of other users (making messages appear to come from someone else).
      • Spreading of misinformation or phishing links (by visually altering message content).
      • Disruption of the chat flow and user experience.
      • Significant loss of user trust in the application.
    • Affected Component: The core message display mechanism of css-only-chat, specifically the CSS rules and HTML structure used to render messages (e.g., elements with classes like .message, .message-author, .message-content, and any associated pseudo-elements). The library's entire styling system is the attack surface.
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Strict Input Sanitization (Application-Level): The application integrating css-only-chat must rigorously sanitize all user inputs that could influence the generated HTML or CSS, even indirectly. This is paramount. Use a whitelist approach, allowing only known-safe characters.
      • Content Security Policy (CSP): Enforce a strict CSP with a style-src directive that only allows the intended CSS file(s) from the css-only-chat library and the application's own controlled CSS. Disallow unsafe-inline and external CSS sources. This is the primary defense against injected CSS.
      • Output Encoding (Application-Level): Ensure that all user-supplied data displayed within the chat is properly HTML-encoded by the application to prevent it from being interpreted as HTML or CSS.
      • Avoid Inline Styles: Minimize or eliminate the use of inline styles (style="...") within the chat's HTML structure generated by the application or the library.
      • Regular Expression for Usernames (Application-Level): If usernames are used in CSS classes (which should be avoided if possible), use a very restrictive regular expression to limit allowed characters.

Threat: CSS-Based History Manipulation

  • Description: An attacker injects CSS that targets the css-only-chat message container or individual message elements to alter the displayed order of messages, hide messages, or create the illusion of deleted messages. This leverages CSS properties like display: none, visibility: hidden, order (with flexbox), position: absolute, and z-index, all of which are likely used by the library for layout. The attacker manipulates the presentation of the history, not the underlying data. This is a direct threat because the library's reliance on CSS for layout makes it vulnerable.
    • Impact:
      • Significant disruption of the conversation flow and context.
      • Censorship of specific messages (making them disappear visually).
      • Creation of a false narrative by reordering messages.
      • Undermining the integrity and trustworthiness of the chat history.
    • Affected Component: The container element holding the messages within the css-only-chat structure (e.g., a <div> with a class like .chat-history or .messages) and the individual message elements within it. CSS rules controlling layout and visibility are the primary targets. The library's layout system is the vulnerability.
    • Risk Severity: High
    • Mitigation Strategies:
      • CSP (as above): A strict CSP is crucial to prevent injected CSS from altering the layout defined by css-only-chat.
      • DOM Integrity Checks (JavaScript): Introduce a small, security-focused JavaScript function that periodically verifies the order and presence of messages against a server-provided list (e.g., by comparing message IDs or timestamps). This is a deviation from "CSS-only," but it's a necessary addition for robust security against this direct threat to the library's functionality.
      • Minimize Dynamic CSS (Library Modification - If Possible): If you have the ability to modify the css-only-chat library itself (or submit a pull request), consider reducing the reliance on easily manipulated CSS features for ordering and visibility. Favor the natural DOM order. This is a proactive, library-level mitigation.
      • Server-Side Rendering (SSR) (Application-Level): If feasible, consider server-side rendering of the chat history. This reduces the reliance on client-side CSS for the initial rendering and makes manipulation more difficult.

Threat: Spoofing Usernames via CSS

  • Description: If css-only-chat renders usernames using CSS (e.g., via ::before or ::after pseudo-elements, or by manipulating class names that determine styling), an attacker could inject CSS to alter the displayed username. This could involve changing the text content, color, or font to mimic another user. This is a direct threat if the library itself handles username display via CSS.
    • Impact:
      • Impersonation of other users, leading to potential abuse or misinformation.
      • Erosion of trust in the chat system's user identification.
    • Affected Component: The CSS rules within css-only-chat that are responsible for rendering usernames, likely involving pseudo-elements or class-based styling applied to elements representing the user.
    • Risk Severity: High
    • Mitigation Strategies:
      • Render Usernames with HTML (Library Modification/Application-Level): The best solution is to modify css-only-chat (or the application integrating it) to render usernames directly within HTML elements (e.g., <span>) rather than relying solely on CSS. This fundamentally removes the vulnerability.
      • Strict Input Sanitization (for usernames) (Application-Level): If usernames must be used in a way that influences CSS, the application must enforce a very restrictive whitelist for allowed username characters.
      • CSP: As with other threats, a strong CSP is essential to prevent injected CSS from modifying the username display.
      • Visually distinct users (Application-Level): Use visually distinct characteristics for users, that are hard to replicate with CSS (e.g. server generated avatars). This provides a fallback visual cue even if CSS is manipulated.