diff --git a/packages/x-chat-headless/src/message/defaultMessagePartRenderers.tsx b/packages/x-chat-headless/src/message/defaultMessagePartRenderers.tsx
index 0fb3a2a4845d3..50895aee01ddc 100644
--- a/packages/x-chat-headless/src/message/defaultMessagePartRenderers.tsx
+++ b/packages/x-chat-headless/src/message/defaultMessagePartRenderers.tsx
@@ -12,6 +12,7 @@ import type {
   ChatToolMessagePart,
 } from '../types/chat-message-parts';
 import type { ChatPartRenderer } from '../renderers/chatPartRenderer';
+import { safeUri } from './parts/partUtils';
 
 function JsonBlock(props: { value: unknown }) {
   const { value } = props;
@@ -61,12 +62,12 @@ export const renderDefaultFilePart: ChatPartRenderer<ChatFileMessagePart> = ({ p
     return <img alt={part.filename ?? ''} src={part.url} />;
   }
 
-  return <a href={part.url}>{part.filename ?? part.url}</a>;
+  return <a href={safeUri(part.url)}>{part.filename ?? part.url}</a>;
 };
 
 export const renderDefaultSourceUrlPart: ChatPartRenderer<ChatSourceUrlMessagePart> = ({
   part,
-}) => <a href={part.url}>{part.title ?? part.url}</a>;
+}) => <a href={safeUri(part.url)}>{part.title ?? part.url}</a>;
 
 export const renderDefaultSourceDocumentPart: ChatPartRenderer<ChatSourceDocumentMessagePart> = ({
   part,
diff --git a/packages/x-chat-headless/src/message/parts/FilePart.tsx b/packages/x-chat-headless/src/message/parts/FilePart.tsx
index 119c48258cfeb..f1b96f5346eed 100644
--- a/packages/x-chat-headless/src/message/parts/FilePart.tsx
+++ b/packages/x-chat-headless/src/message/parts/FilePart.tsx
@@ -6,6 +6,7 @@ import type { ChatFileMessagePart } from '../../types/chat-message-parts';
 import type { ChatPartRenderer, ChatPartRendererProps } from '../../renderers/chatPartRenderer';
 import type { ChatRole } from '../../types/chat-entities';
 import { useMessageContentTabIndex } from '../../message-list/internals/MessageRovingContext';
+import { safeUri } from './partUtils';
 
 export interface FilePartOwnerState {
   image: boolean;
@@ -113,7 +114,7 @@ export const FilePart = React.forwardRef(function FilePart(
 
   return (
     <Root {...rootProps}>
-      <LinkSlot href={part.url} rel="noreferrer noopener" target="_blank" {...linkProps}>
+      <LinkSlot href={safeUri(part.url)} rel="noreferrer noopener" target="_blank" {...linkProps}>
         {ownerState.image ? (
           <Preview alt={part.filename ?? ''} src={part.url} {...previewProps} />
         ) : (
diff --git a/packages/x-chat-headless/src/message/parts/MessageParts.test.tsx b/packages/x-chat-headless/src/message/parts/MessageParts.test.tsx
index 1d46c91dd8c4d..3bc4029a8419a 100644
--- a/packages/x-chat-headless/src/message/parts/MessageParts.test.tsx
+++ b/packages/x-chat-headless/src/message/parts/MessageParts.test.tsx
@@ -18,9 +18,14 @@ import {
 } from '../defaultMessagePartRenderers';
 import { MessageContent } from '../MessageContent';
 import { MessageRoot } from '../MessageRoot';
+import { SourceUrlPart } from './SourceUrlPart';
+import { FilePart } from './FilePart';
 
 const { render } = createRenderer();
 
+// eslint-disable-next-line no-script-url -- intentional attacker-controlled fixture for sanitization tests
+const SCRIPT_URL = 'javascript:alert(document.cookie)';
+
 function createAdapter(): ChatAdapter {
   return {
     async sendMessage() {
@@ -239,6 +244,43 @@ describe('FilePart', () => {
 
     expect(screen.getByText('https://example.com/doc.pdf')).not.to.equal(null);
   });
+
+  it('neutralizes javascript: URLs in the link href', () => {
+    renderWithMessage({
+      id: 'm1',
+      role: 'assistant',
+      parts: [
+        {
+          type: 'file',
+          mediaType: 'application/pdf',
+          url: SCRIPT_URL,
+        },
+      ],
+    });
+
+    const link = screen.getByText(SCRIPT_URL).closest('a');
+
+    expect(link).not.to.equal(null);
+    expect(link!.getAttribute('href')).to.equal('');
+  });
+
+  it('keeps data: image sources on the img src', () => {
+    const dataUrl = 'data:image/png;base64,iVBORw0KGgo=';
+    renderWithMessage({
+      id: 'm1',
+      role: 'assistant',
+      parts: [
+        {
+          type: 'file',
+          mediaType: 'image/png',
+          url: dataUrl,
+          filename: 'inline.png',
+        },
+      ],
+    });
+
+    expect(screen.getByAltText('inline.png')).to.have.attribute('src', dataUrl);
+  });
 });
 
 describe('SourceUrlPart', () => {
@@ -277,6 +319,62 @@ describe('SourceUrlPart', () => {
 
     expect(screen.getByText('https://mui.com/x')).not.to.equal(null);
   });
+
+  it('neutralizes javascript: URLs in the link href', () => {
+    renderWithMessage({
+      id: 'm1',
+      role: 'assistant',
+      parts: [
+        {
+          type: 'source-url',
+          sourceId: 's1',
+          url: SCRIPT_URL,
+        },
+      ],
+    });
+
+    const link = screen.getByText(SCRIPT_URL).closest('a');
+
+    expect(link).not.to.equal(null);
+    expect(link!.getAttribute('href')).to.equal('');
+  });
+});
+
+describe('Part primitives URL sanitization', () => {
+  it('SourceUrlPart neutralizes javascript: URLs in href', () => {
+    render(
+      <SourceUrlPart
+        index={0}
+        message={{ id: 'm1', role: 'assistant', parts: [] }}
+        part={{ type: 'source-url', sourceId: 's1', url: SCRIPT_URL }}
+      />,
+    );
+
+    const link = screen.getByText(SCRIPT_URL).closest('a');
+
+    expect(link).not.to.equal(null);
+    expect(link!.getAttribute('href')).to.equal('');
+  });
+
+  it('FilePart neutralizes javascript: URLs in href', () => {
+    render(
+      <FilePart
+        index={0}
+        message={{ id: 'm1', role: 'assistant', parts: [] }}
+        part={{
+          type: 'file',
+          mediaType: 'application/pdf',
+          url: SCRIPT_URL,
+          filename: 'x.pdf',
+        }}
+      />,
+    );
+
+    const link = screen.getByText('x.pdf').closest('a');
+
+    expect(link).not.to.equal(null);
+    expect(link!.getAttribute('href')).to.equal('');
+  });
 });
 
 describe('SourceDocumentPart', () => {
diff --git a/packages/x-chat-headless/src/message/parts/SourceUrlPart.tsx b/packages/x-chat-headless/src/message/parts/SourceUrlPart.tsx
index a19c53c162f1b..f06622e345dc2 100644
--- a/packages/x-chat-headless/src/message/parts/SourceUrlPart.tsx
+++ b/packages/x-chat-headless/src/message/parts/SourceUrlPart.tsx
@@ -6,6 +6,7 @@ import type { ChatPartRenderer, ChatPartRendererProps } from '../../renderers/ch
 import type { ChatRole } from '../../types/chat-entities';
 import type { ChatSourceUrlMessagePart } from '../../types/chat-message-parts';
 import { useMessageContentTabIndex } from '../../message-list/internals/MessageRovingContext';
+import { safeUri } from './partUtils';
 
 export interface SourceUrlPartOwnerState {
   messageId: string;
@@ -104,7 +105,7 @@ export const SourceUrlPart = React.forwardRef(function SourceUrlPart(
       <Icon {...iconProps}>
         <ExternalLinkIcon />
       </Icon>
-      <LinkSlot href={part.url} rel="noreferrer noopener" target="_blank" {...linkProps}>
+      <LinkSlot href={safeUri(part.url)} rel="noreferrer noopener" target="_blank" {...linkProps}>
         {part.title ?? part.url}
       </LinkSlot>
     </Root>