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security(sanitization): mitigate mutation XSS by replacing regex-base… #1812

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Merged
csxark merged 1 commit into from
Aug 31, 2026
Merged

security(sanitization): mitigate mutation XSS by replacing regex-base… #1812

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36 changes: 24 additions & 12 deletions lib/security/inputSanitization.ts
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Original file line number Diff line number Diff line change
@@ -1,3 +1,12 @@
import DOMPurify from "dompurify";
import { JSDOM } from "jsdom";

const domWindow =
typeof window !== "undefined"
? (window as unknown as Window & typeof globalThis)
: (new JSDOM("").window as unknown as Window & typeof globalThis);
const purifier = DOMPurify(domWindow);

export type SanitizedInputKind =
| "plain-text"
| "hex"
Expand All @@ -14,6 +23,8 @@ export interface SanitizationOptions {
collapseWhitespace?: boolean;
preserveCase?: boolean;
escapeHtml?: boolean;
allowedTags?: string[];
allowedAttributes?: string[];
}

export interface SanitizationResult {
Expand Down Expand Up @@ -94,17 +105,18 @@ export function sanitizePlainText(value: unknown, options: SanitizationOptions =

let val = result.value;

// 1. Remove dangerous HTML tags completely
val = val.replace(/<\/?(script|img|svg|iframe|object|embed|body|form|input)[^>]*>/gi, "");

// 2. Remove dangerous event listener attributes
val = val.replace(/(on[a-z]+)\s*=\s*("[^"]*"|'[^']*'|[^>\s]*)/gi, "");

// 3. Neutralize dangerous URL protocols
val = val.replace(/(javascript|data|vbscript)\s*:/gi, "$1_blocked:");

// 4. Escape HTML if requested (default is true)
if (options.escapeHtml !== false) {
if (options.escapeHtml === false) {
const purifyConfig = {
ALLOWED_TAGS: options.allowedTags || ["b", "i", "em", "strong", "p", "br", "span"],
ALLOWED_ATTR: options.allowedAttributes || ["class", "id"],
FORCE_BODY: true,
RETURN_DOM: false,
};
val = purifier.sanitize(val, purifyConfig);
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MILAN-123865 marked this conversation as resolved.
} else {
// Neutralize dangerous event listener attributes and URL protocols for plain-text escaping
val = val.replace(/(on[a-z]+)\s*=\s*("[^"]*"|'[^']*'|[^>\s]*)/gi, "");
val = val.replace(/(javascript|data|vbscript)\s*:/gi, "$1_blocked:");
val = escapeHtml(val);
}

Expand Down Expand Up @@ -233,7 +245,7 @@ export function sanitizeMarkdown(value: unknown, maxLength = DEFAULT_MAX_LENGTH)
});

const withoutDangerousLinks = plain.value.replace(
/\]\(\s*(javascript:|data:text\/html|vbscript:)[^)]+\)/gi,
/\]\(\s*(javascript:|javascript_blocked:|data:text\/html|vbscript:)[^)]+\)/gi,
"](#)",
);
const withoutRawHtml = withoutDangerousLinks.replace(/&lt;\/?(script|iframe|object|embed|style)[^&]*&gt;/gi, "");
Expand Down
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