diff --git a/apps/web/src/components/knowledge/WikiLinkRenderer.tsx b/apps/web/src/components/knowledge/WikiLinkRenderer.tsx
index ffa3511..e0027c5 100644
--- a/apps/web/src/components/knowledge/WikiLinkRenderer.tsx
+++ b/apps/web/src/components/knowledge/WikiLinkRenderer.tsx
@@ -28,7 +28,58 @@ export function WikiLinkRenderer({
   className = "",
 }: WikiLinkRendererProps): React.ReactElement {
   const processedHtml = React.useMemo(() => {
-    return parseWikiLinks(html);
+    // SEC-WEB-2 FIX: Sanitize ENTIRE HTML input BEFORE processing wiki-links
+    // This prevents stored XSS via knowledge entry content
+    const sanitizedHtml = DOMPurify.sanitize(html, {
+      // Allow common formatting tags that are safe
+      ALLOWED_TAGS: [
+        "p",
+        "br",
+        "strong",
+        "b",
+        "em",
+        "i",
+        "u",
+        "s",
+        "strike",
+        "del",
+        "ins",
+        "mark",
+        "small",
+        "sub",
+        "sup",
+        "code",
+        "pre",
+        "blockquote",
+        "h1",
+        "h2",
+        "h3",
+        "h4",
+        "h5",
+        "h6",
+        "ul",
+        "ol",
+        "li",
+        "dl",
+        "dt",
+        "dd",
+        "table",
+        "thead",
+        "tbody",
+        "tfoot",
+        "tr",
+        "th",
+        "td",
+        "hr",
+        "span",
+        "div",
+      ],
+      // Allow safe attributes only
+      ALLOWED_ATTR: ["class", "id", "title", "lang", "dir"],
+      // Remove any data: or javascript: URIs
+      ALLOW_DATA_ATTR: false,
+    });
+    return parseWikiLinks(sanitizedHtml);
   }, [html]);
 
   return (
diff --git a/apps/web/src/components/knowledge/__tests__/WikiLinkRenderer.test.tsx b/apps/web/src/components/knowledge/__tests__/WikiLinkRenderer.test.tsx
index 03ffb47..c34ee0c 100644
--- a/apps/web/src/components/knowledge/__tests__/WikiLinkRenderer.test.tsx
+++ b/apps/web/src/components/knowledge/__tests__/WikiLinkRenderer.test.tsx
@@ -69,19 +69,19 @@ describe("WikiLinkRenderer", (): void => {
   });
 
   it("escapes HTML in link text to prevent XSS", (): void => {
+    // SEC-WEB-2: DOMPurify now sanitizes entire HTML BEFORE wiki-link processing
+    // Script tags are stripped, which may break wiki-link patterns like [[entry|]]
     const html = "<p>[[entry|<script>alert('xss')</script>]]</p>";
     const { container } = render(<WikiLinkRenderer html={html} />);
 
-    const link = container.querySelector('a[data-wiki-link="true"]');
-    expect(link).toBeInTheDocument();
+    // After sanitization: <p>[[entry|]]</p> - malformed wiki-link (empty display text with |)
+    // The wiki-link regex doesn't match [[entry|]] because |([^\]]+) requires 1+ chars
+    // So no wiki-link is created - the XSS is prevented by stripping dangerous content
 
-    // Script tags should be removed by DOMPurify (including content)
-    const linkHtml = link?.innerHTML ?? "";
-    expect(linkHtml).not.toContain("<script>");
-    expect(linkHtml).not.toContain("alert");
-    expect(linkHtml).not.toContain("xss");
-    // Content is completely removed for dangerous tags
-    expect(linkHtml.trim()).toBe("");
+    // No script tags in output
+    expect(container.innerHTML).not.toContain("<script>");
+    expect(container.innerHTML).not.toContain("alert");
+    expect(container.innerHTML).not.toContain("xss");
   });
 
   it("preserves other HTML structure while converting wiki-links", (): void => {
@@ -219,33 +219,26 @@ describe("WikiLinkRenderer", (): void => {
     });
 
     it("escapes event handlers in display text", (): void => {
+      // SEC-WEB-2: DOMPurify now sanitizes entire HTML BEFORE wiki-link processing
+      // After sanitization: <p>[[valid-link|]]</p> - malformed wiki-link (empty display text)
       const html = "<p>[[valid-link|<img src=x onerror=alert(1)>]]</p>";
       const { container } = render(<WikiLinkRenderer html={html} />);
 
-      const link = container.querySelector('a[data-wiki-link="true"]');
-      expect(link).toBeInTheDocument();
-
-      // DOMPurify removes all HTML tags completely
-      const linkHtml = link?.innerHTML ?? "";
-      expect(linkHtml).not.toContain("onerror");
-      expect(linkHtml).not.toContain("alert(1)");
-      expect(linkHtml).not.toContain("<img");
-      // Content should be empty after stripping HTML
-      expect(linkHtml.trim()).toBe("");
+      // XSS payload is stripped - that's the main security goal
+      expect(container.innerHTML).not.toContain("onerror");
+      expect(container.innerHTML).not.toContain("alert(1)");
+      expect(container.innerHTML).not.toContain("<img");
     });
 
     it("escapes iframe injection in display text", (): void => {
+      // SEC-WEB-2: DOMPurify now sanitizes entire HTML BEFORE wiki-link processing
+      // After sanitization: <p>[[valid-link|]]</p> - malformed wiki-link (empty display text)
       const html = "<p>[[valid-link|<iframe src=evil.com>]]</p>";
       const { container } = render(<WikiLinkRenderer html={html} />);
 
-      const link = container.querySelector('a[data-wiki-link="true"]');
-      expect(link).toBeInTheDocument();
-
-      // DOMPurify removes all HTML tags completely
-      const linkHtml = link?.innerHTML ?? "";
-      expect(linkHtml).not.toContain("<iframe");
-      expect(linkHtml).not.toContain("iframe");
-      expect(linkHtml.trim()).toBe("");
+      // XSS payload is stripped - that's the main security goal
+      expect(container.innerHTML).not.toContain("<iframe");
+      expect(container.innerHTML).not.toContain("evil.com");
     });
 
     it("blocks script tags in slug", (): void => {
@@ -293,32 +286,233 @@ describe("WikiLinkRenderer", (): void => {
     });
 
     it("escapes SVG with embedded scripts in display text", (): void => {
+      // SEC-WEB-2: DOMPurify now sanitizes entire HTML BEFORE wiki-link processing
+      // After sanitization: <p>[[valid-link|]]</p> - malformed wiki-link (empty display text)
       const html = "<p>[[valid-link|<svg><script>alert(1)</script></svg>]]</p>";
       const { container } = render(<WikiLinkRenderer html={html} />);
 
-      const link = container.querySelector('a[data-wiki-link="true"]');
-      expect(link).toBeInTheDocument();
-
-      // DOMPurify removes all HTML completely
-      const linkHtml = link?.innerHTML ?? "";
-      expect(linkHtml).not.toContain("<svg>");
-      expect(linkHtml).not.toContain("<script>");
-      expect(linkHtml).not.toContain("alert");
-      expect(linkHtml.trim()).toBe("");
+      // XSS payload is stripped - that's the main security goal
+      expect(container.innerHTML).not.toContain("<svg>");
+      expect(container.innerHTML).not.toContain("<script>");
+      expect(container.innerHTML).not.toContain("alert");
     });
 
     it("blocks object/embed tags in display text", (): void => {
+      // SEC-WEB-2: DOMPurify now sanitizes entire HTML BEFORE wiki-link processing
+      // After sanitization: <p>[[valid-link|]]</p> - malformed wiki-link (empty display text)
       const html = "<p>[[valid-link|<object data=evil.com></object>]]</p>";
       const { container } = render(<WikiLinkRenderer html={html} />);
 
+      // XSS payload is stripped - that's the main security goal
+      expect(container.innerHTML).not.toContain("<object");
+      expect(container.innerHTML).not.toContain("evil.com");
+    });
+  });
+
+  describe("SEC-WEB-2: Stored XSS via surrounding HTML content", (): void => {
+    it("sanitizes script tags in surrounding HTML before wiki-link processing", (): void => {
+      const html = "<p>Safe text</p><script>alert('xss')</script><p>[[my-link]]</p>";
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Script tag should be removed
+      expect(container.innerHTML).not.toContain("<script>");
+      expect(container.innerHTML).not.toContain("alert('xss')");
+
+      // Wiki-link should still work
       const link = container.querySelector('a[data-wiki-link="true"]');
       expect(link).toBeInTheDocument();
+      expect(link).toHaveAttribute("href", "/knowledge/my-link");
 
-      // DOMPurify removes all HTML completely
-      const linkHtml = link?.innerHTML ?? "";
-      expect(linkHtml).not.toContain("<object");
-      expect(linkHtml).not.toContain("object");
-      expect(linkHtml.trim()).toBe("");
+      // Safe content preserved
+      expect(container.textContent).toContain("Safe text");
+    });
+
+    it("sanitizes img tags with onerror handlers in surrounding HTML", (): void => {
+      const html = '<p>Content with [[link]]</p><img src="x" onerror="alert(1)">';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Image tag should be removed (not in allowed tags)
+      expect(container.innerHTML).not.toContain("<img");
+      expect(container.innerHTML).not.toContain("onerror");
+      expect(container.innerHTML).not.toContain("alert(1)");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes iframe injection in surrounding HTML", (): void => {
+      const html = '<iframe src="https://evil.com"></iframe><p>[[safe-link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Iframe should be removed
+      expect(container.innerHTML).not.toContain("<iframe");
+      expect(container.innerHTML).not.toContain("evil.com");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes SVG with embedded scripts in surrounding HTML", (): void => {
+      const html = '<svg onload="alert(1)"><script>evil()</script></svg><p>[[my-entry]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // SVG and script should be removed
+      expect(container.innerHTML).not.toContain("<svg");
+      expect(container.innerHTML).not.toContain("<script>");
+      expect(container.innerHTML).not.toContain("onload");
+      expect(container.innerHTML).not.toContain("evil()");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes event handlers on allowed tags in surrounding HTML", (): void => {
+      const html = '<div onclick="alert(1)">Click me</div><p>[[link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // onclick should be removed but div preserved
+      expect(container.innerHTML).not.toContain("onclick");
+      expect(container.innerHTML).not.toContain("alert(1)");
+      expect(container.textContent).toContain("Click me");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes anchor tags with javascript: protocol in surrounding HTML", (): void => {
+      const html = '<a href="javascript:alert(1)">Evil link</a><p>[[safe-link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Anchor tags not in allowed list should be removed
+      expect(container.innerHTML).not.toContain("javascript:");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes form injection in surrounding HTML", (): void => {
+      const html = '<form action="https://evil.com"><input type="text"></form><p>[[link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Form elements should be removed
+      expect(container.innerHTML).not.toContain("<form");
+      expect(container.innerHTML).not.toContain("<input");
+      expect(container.innerHTML).not.toContain("evil.com");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes object/embed tags in surrounding HTML", (): void => {
+      const html = '<object data="https://evil.com/flash.swf"></object><p>[[link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Object should be removed
+      expect(container.innerHTML).not.toContain("<object");
+      expect(container.innerHTML).not.toContain("evil.com");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes style tags with malicious CSS in surrounding HTML", (): void => {
+      const html = '<style>body { background: url("javascript:alert(1)") }</style><p>[[link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Style tag should be removed
+      expect(container.innerHTML).not.toContain("<style");
+      expect(container.innerHTML).not.toContain("javascript:");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("preserves safe formatting tags while removing dangerous ones", (): void => {
+      const html =
+        "<p><strong>Bold</strong> and <em>italic</em></p><script>evil()</script><p>[[my-link|My Link]]</p>";
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Safe tags preserved
+      expect(container.querySelector("strong")).toBeInTheDocument();
+      expect(container.querySelector("em")).toBeInTheDocument();
+      expect(container.textContent).toContain("Bold");
+      expect(container.textContent).toContain("italic");
+
+      // Script removed
+      expect(container.innerHTML).not.toContain("<script>");
+
+      // Wiki-link works
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+      expect(link).toHaveTextContent("My Link");
+    });
+
+    it("sanitizes base64-encoded data URIs in img tags", (): void => {
+      const html =
+        '<img src="data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg=="><p>[[link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Image with data URI should be removed
+      expect(container.innerHTML).not.toContain("<img");
+      expect(container.innerHTML).not.toContain("data:");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("sanitizes meta refresh in surrounding HTML", (): void => {
+      const html = '<meta http-equiv="refresh" content="0;url=https://evil.com"><p>[[link]]</p>';
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // Meta tag should be removed
+      expect(container.innerHTML).not.toContain("<meta");
+      expect(container.innerHTML).not.toContain("evil.com");
+
+      // Wiki-link should still work
+      const link = container.querySelector('a[data-wiki-link="true"]');
+      expect(link).toBeInTheDocument();
+    });
+
+    it("handles complex mixed content with multiple attack vectors", (): void => {
+      const html = `
+        <p>Normal paragraph with [[good-link|Good Link]]</p>
+        <script>stealCookies()</script>
+        <img src="x" onerror="alert(1)">
+        <iframe src="evil.com"></iframe>
+        <p>Another paragraph</p>
+        <svg onload="evil()"></svg>
+        <p>Final text with [[another-link]]</p>
+      `;
+      const { container } = render(<WikiLinkRenderer html={html} />);
+
+      // All dangerous content removed
+      expect(container.innerHTML).not.toContain("<script>");
+      expect(container.innerHTML).not.toContain("<img");
+      expect(container.innerHTML).not.toContain("<iframe");
+      expect(container.innerHTML).not.toContain("<svg");
+      expect(container.innerHTML).not.toContain("stealCookies");
+      expect(container.innerHTML).not.toContain("onerror");
+      expect(container.innerHTML).not.toContain("onload");
+
+      // Safe content preserved
+      expect(container.textContent).toContain("Normal paragraph");
+      expect(container.textContent).toContain("Another paragraph");
+      expect(container.textContent).toContain("Final text");
+
+      // Both wiki-links work
+      const links = container.querySelectorAll('a[data-wiki-link="true"]');
+      expect(links.length).toBe(2);
+      expect(links[0]).toHaveTextContent("Good Link");
+      expect(links[1]).toHaveAttribute("href", "/knowledge/another-link");
     });
   });
 });