diff --git a/apps/api/src/files/files.e2e.db.test.ts b/apps/api/src/files/files.e2e.db.test.ts
index d29527f..be3cab9 100644
--- a/apps/api/src/files/files.e2e.db.test.ts
+++ b/apps/api/src/files/files.e2e.db.test.ts
@@ -394,6 +394,54 @@ describe.skipIf(!hasTestDb)('files (e2e, issue #27)', () => {
     expect(openOrphan.headers['content-disposition']).toContain('filename="lose-datei.pdf"');
   });
 
+  it('blocks uploads to classified pages server-side when the policy says so (issue #213)', async () => {
+    const settings = app.get(InstanceSettingsService);
+    const page = await api()
+      .post(`/api/v1/ponds/${pondId}/pages`)
+      .set('Cookie', ownerCookie)
+      .send({ title: `Blocked Uploads ${suffix}` })
+      .expect(201);
+    await prisma.page.update({
+      where: { id: page.body.id as string },
+      data: { classification: 'VS_NFD' },
+    });
+
+    // Default policy `warn`: the upload is allowed (the UI shows the notice).
+    await api()
+      .post(`/api/v1/pages/${page.body.id}/files`)
+      .set('Cookie', ownerCookie)
+      .attach('file', Buffer.from('%PDF-1.4 warned upload'), 'warned.pdf')
+      .expect(201);
+
+    await settings.set('classification.uploadPolicy', 'block', 'test');
+    try {
+      // Enforced server-side, not only in the UI.
+      const blocked = await api()
+        .post(`/api/v1/pages/${page.body.id}/files`)
+        .set('Cookie', ownerCookie)
+        .attach('file', Buffer.from('%PDF-1.4 blocked upload'), 'blocked.pdf')
+        .expect(403);
+      expect((blocked.body as { code: string }).code).toBe('classified_upload_blocked');
+
+      // Unclassified pages stay uploadable under `block`.
+      const open = await api()
+        .post(`/api/v1/ponds/${pondId}/pages`)
+        .set('Cookie', ownerCookie)
+        .send({ title: `Open Uploads ${suffix}` })
+        .expect(201);
+      await api()
+        .post(`/api/v1/pages/${open.body.id}/files`)
+        .set('Cookie', ownerCookie)
+        .attach('file', Buffer.from('%PDF-1.4 open upload'), 'open.pdf')
+        .expect(201);
+    } finally {
+      await settings.set('classification.uploadPolicy', 'warn', 'test');
+      await prisma.instanceSetting.deleteMany({
+        where: { key: 'classification.uploadPolicy' },
+      });
+    }
+  });
+
   it('pond file manager reports usage, orphans, and page links (#61)', async () => {
     const page = await api()
       .post(`/api/v1/ponds/${pondId}/pages`)
diff --git a/apps/api/src/files/files.service.ts b/apps/api/src/files/files.service.ts
index 7adff61..2be721e 100644
--- a/apps/api/src/files/files.service.ts
+++ b/apps/api/src/files/files.service.ts
@@ -3,6 +3,7 @@ import { Readable } from 'node:stream';
 
 import {
   BadRequestException,
+  ForbiddenException,
   Injectable,
   InternalServerErrorException,
   NotFoundException,
@@ -205,6 +206,16 @@ export class FilesService {
   ): Promise<AttachmentView> {
     const page = await this.prisma.page.findFirst({ where: { id: pageId } });
     if (!page) throw new NotFoundException();
+    // Attaching to a classified page (issue #213, ADR 0022): the file will
+    // inherit a classification its content cannot carry (#212). The UI warns;
+    // the instance can harden the warning into a server-side block — enforced
+    // HERE, not only client-side.
+    if (page.classification === 'VS_NFD') {
+      const policy = await this.settings.get('classification.uploadPolicy');
+      if (policy === 'block') {
+        throw new ForbiddenException({ code: 'classified_upload_blocked' });
+      }
+    }
     return this.upload(user, page.pondId, file, page.id);
   }
 
diff --git a/apps/api/src/settings/instance-settings.service.ts b/apps/api/src/settings/instance-settings.service.ts
index 67f2571..d9aa7f7 100644
--- a/apps/api/src/settings/instance-settings.service.ts
+++ b/apps/api/src/settings/instance-settings.service.ts
@@ -57,6 +57,11 @@ export const INSTANCE_SETTINGS = {
   // parent page (#205) wins over this default. The marking is not a
   // protection mechanism — permissions ignore it.
   'classification.newPageDefault': z.enum(['unclassified', 'vs_nfd']).default('unclassified'),
+  // Attaching files to a classified page (issue #213, ADR 0022): the UI
+  // always warns (the file inherits a classification its content cannot
+  // carry, #212); `block` hardens the warning into a server-side rejection.
+  // Default `warn` — blocking is the reference-configuration choice (#227).
+  'classification.uploadPolicy': z.enum(['warn', 'block']).default('warn'),
   // Non-image upload allowlist (ADR 0011, issue #61): lowercase extensions
   // without the dot. Images are always allowed regardless; SVG is governed
   // by `upload.svgPolicy`. Normalized (lowercased, dot-stripped, deduped) so
diff --git a/apps/web/e2e/attachments.spec.ts b/apps/web/e2e/attachments.spec.ts
index d237726..455973d 100644
--- a/apps/web/e2e/attachments.spec.ts
+++ b/apps/web/e2e/attachments.spec.ts
@@ -109,3 +109,19 @@ test('pond file manager shows usage and flags an orphan (Pond Admin)', async ({
 
   await context.close();
 });
+
+test('shows the classified-upload warning on a classified page (issue #213)', async ({
+  browser,
+}) => {
+  const context = await contextForUser(browser, BASE_URL, 'fixture-user');
+  const page = await context.newPage();
+  await page.goto('/p/content-fixtures/classified-note');
+  await openAttachments(page);
+  // The persistent warning names the consequence; the wording is the fixed
+  // marking formula (ADR 0022), not localized.
+  await expect(page.locator('.attachments-panel__warning')).toBeVisible();
+  await expect(page.locator('.attachments-panel__warning')).toContainText(
+    'VS – NUR FÜR DEN DIENSTGEBRAUCH',
+  );
+  await context.close();
+});
diff --git a/apps/web/src/files/AttachmentsPanel.tsx b/apps/web/src/files/AttachmentsPanel.tsx
index 8ba21d6..b928cb8 100644
--- a/apps/web/src/files/AttachmentsPanel.tsx
+++ b/apps/web/src/files/AttachmentsPanel.tsx
@@ -1,4 +1,4 @@
-import type { AttachmentListItemView } from '@dorfteich/shared';
+import type { AttachmentListItemView, PageClassification } from '@dorfteich/shared';
 import { useQuery, useQueryClient } from '@tanstack/react-query';
 import type { Editor } from '@tiptap/react';
 import { useRef, useState } from 'react';
@@ -19,11 +19,16 @@ export function AttachmentsPanel({
   pageId,
   editor,
   canEdit,
+  classification,
   onClose,
 }: {
   pageId: string;
   editor: Editor | null;
   canEdit: boolean;
+  /** VS-NfD level of the page (issue #213): a classified page shows the
+   * upload warning naming the consequence — attachments inherit a level
+   * their content cannot carry (#212). */
+  classification?: PageClassification;
   onClose: () => void;
 }): React.JSX.Element {
   const { t } = useTranslation('files');
@@ -96,6 +101,12 @@ export function AttachmentsPanel({
 
       <FormError error={error} />
 
+      {canEdit && classification === 'vs_nfd' && (
+        <p className="attachments-panel__warning" role="note">
+          {t('classifiedUploadWarning')}
+        </p>
+      )}
+
       {canEdit && (
         <div className="attachments-panel__upload">
           <input
diff --git a/apps/web/src/pages/AdminSettingsPage.tsx b/apps/web/src/pages/AdminSettingsPage.tsx
index 978c295..62a0eb0 100644
--- a/apps/web/src/pages/AdminSettingsPage.tsx
+++ b/apps/web/src/pages/AdminSettingsPage.tsx
@@ -29,6 +29,7 @@ interface InstanceSettings {
   'upload.allowedExtensions': string[];
   'upload.svgPolicy': 'reject' | 'sanitize';
   'classification.newPageDefault': 'unclassified' | 'vs_nfd';
+  'classification.uploadPolicy': 'warn' | 'block';
   'legal.imprint': string;
   'legal.privacyPolicy': string;
   'home.content': string;
@@ -101,6 +102,15 @@ export function AdminSettingsPage(): React.JSX.Element {
                 <option value="vs_nfd">{t('settings:admin.classificationVsNfd')}</option>
               </select>
             </Field>
+            <Field
+              label={t('settings:admin.uploadPolicy')}
+              hint={t('settings:admin.uploadPolicyHelp')}
+            >
+              <select {...form.register('classification.uploadPolicy')}>
+                <option value="warn">{t('settings:admin.uploadPolicyWarn')}</option>
+                <option value="block">{t('settings:admin.uploadPolicyBlock')}</option>
+              </select>
+            </Field>
             <button type="submit" className="button" disabled={form.formState.isSubmitting}>
               {t('settings:admin.save')}
             </button>
diff --git a/apps/web/src/pages/PageEditorPage.tsx b/apps/web/src/pages/PageEditorPage.tsx
index 573e7e2..3fbdd8f 100644
--- a/apps/web/src/pages/PageEditorPage.tsx
+++ b/apps/web/src/pages/PageEditorPage.tsx
@@ -1,5 +1,10 @@
 import { DEFAULT_FONTS, extractOutline } from '@dorfteich/shared';
-import type { PageListItemView, PageStateView, PondView } from '@dorfteich/shared';
+import type {
+  PageClassification,
+  PageListItemView,
+  PageStateView,
+  PondView,
+} from '@dorfteich/shared';
 import { useQuery, useQueryClient } from '@tanstack/react-query';
 import { Collaboration } from '@tiptap/extension-collaboration';
 import { EditorContent, useEditor } from '@tiptap/react';
@@ -126,6 +131,8 @@ interface ResolvedPage {
   pondId: string;
   slug: string;
   title: string;
+  /** VS-NfD level (issue #213); undefined for the offline-cache fallback. */
+  classification?: PageClassification;
 }
 
 function PageEditor({
@@ -305,6 +312,7 @@ function PageEditor({
               pageId={page.id}
               editor={editor}
               canEdit={canEdit}
+              classification={page.classification}
               onClose={onCloseAttachments}
             />
           )}
@@ -421,7 +429,13 @@ export function PageEditorPage(): React.JSX.Element {
   const offlineCached = !navigator.onLine && !page.data ? recallPage(pondSlug, pageSlug) : null;
 
   const resolved: ResolvedPage | null = page.data
-    ? { id: page.data.id, pondId: page.data.pondId, slug: page.data.slug, title: page.data.title }
+    ? {
+        id: page.data.id,
+        pondId: page.data.pondId,
+        slug: page.data.slug,
+        title: page.data.title,
+        classification: page.data.classification,
+      }
     : offlineCached
       ? {
           id: offlineCached.pageId,
diff --git a/apps/web/src/styles/base.css b/apps/web/src/styles/base.css
index 1e5fadc..eee2963 100644
--- a/apps/web/src/styles/base.css
+++ b/apps/web/src/styles/base.css
@@ -3071,6 +3071,17 @@ ul[data-type='task_list'] li p:last-of-type {
   margin: 0;
 }
 
+/* Upload warning on classified pages (issue #213, ADR 0022) — a persistent
+   note, not a dismissable toast: the consequence applies to every upload. */
+.attachments-panel__warning {
+  margin: 0 0 var(--space-2);
+  padding: var(--space-2);
+  border: 1px solid var(--color-border);
+  border-left: 3px solid currentColor;
+  font-size: 0.85rem;
+  color: var(--color-text);
+}
+
 .attachments-panel__upload {
   display: flex;
   align-items: center;
diff --git a/docs/vs-nfd/20-massnahmenplan.md b/docs/vs-nfd/20-massnahmenplan.md
index ee91ef2..d83c10b 100644
--- a/docs/vs-nfd/20-massnahmenplan.md
+++ b/docs/vs-nfd/20-massnahmenplan.md
@@ -59,7 +59,7 @@ _Meilenstein: `M26 — VS-NfD: classification metadata`_
   - [x] Markdown-ZIP (Frontmatter + Aufdruck) · 1 AT · #210
   - [x] Atom-Feeds, Public-API, Suchergebnisse, No-JS-Shell · 2–3 AT · #211
   - [x] Attachment-Download (Dateiname-Präfix + Begleitdatei) · 1–2 AT · #212
-- [ ] Warnung/Sperre beim Anhängen an eingestufte Seiten · 1 AT · #213
+- [x] Warnung/Sperre beim Anhängen an eingestufte Seiten · 1 AT · #213
 
 ### P1-3 Verifizierter Offline-/Airgap-Pfad · 8–10 AT ⟵ neu aus Roadmap
 
diff --git a/packages/shared/i18n/de/errors.json b/packages/shared/i18n/de/errors.json
index 03d1b62..bd32ec2 100644
--- a/packages/shared/i18n/de/errors.json
+++ b/packages/shared/i18n/de/errors.json
@@ -110,5 +110,6 @@
   "backup_set_not_found": "Das gewählte Backup-Set wurde nicht gefunden.",
   "scope_required": "Dieses API-Token hat nicht den erforderlichen Scope.",
   "pond_not_found": "Der Teich existiert nicht.",
-  "classification_lower_forbidden": "Zum Herabstufen der Einstufung fehlt die Berechtigung (Teich-Admin erforderlich)."
+  "classification_lower_forbidden": "Zum Herabstufen der Einstufung fehlt die Berechtigung (Teich-Admin erforderlich).",
+  "classified_upload_blocked": "Uploads auf eingestufte Seiten sind auf dieser Instanz blockiert."
 }
diff --git a/packages/shared/i18n/de/files.json b/packages/shared/i18n/de/files.json
index e39f374..735e498 100644
--- a/packages/shared/i18n/de/files.json
+++ b/packages/shared/i18n/de/files.json
@@ -19,5 +19,6 @@
     "svgSanitize": "Bereinigen (Skripte entfernen)",
     "svgReject": "Ablehnen",
     "save": "Upload-Einstellungen speichern"
-  }
+  },
+  "classifiedUploadWarning": "Diese Seite ist als „VS – NUR FÜR DEN DIENSTGEBRAUCH\" eingestuft. Angehängte Dateien erben die Einstufung; die Datei selbst trägt im Inhalt keine Kennzeichnung (nur Dateinamens-Präfix und Begleitdatei beim Download)."
 }
diff --git a/packages/shared/i18n/de/settings.json b/packages/shared/i18n/de/settings.json
index 37ec6b6..630d92e 100644
--- a/packages/shared/i18n/de/settings.json
+++ b/packages/shared/i18n/de/settings.json
@@ -52,7 +52,11 @@
     "newPageClassification": "Einstufung neuer Seiten",
     "newPageClassificationHelp": "Standard-Einstufung (VS-NfD-Kennzeichnung) für neu angelegte Seiten. Die Kennzeichnung ist keine Zugriffskontrolle; die Trennung von Einstufungsniveaus leistet die Umgebung (eine Instanz je Niveau).",
     "classificationUnclassified": "Offen — keine Kennzeichnung",
-    "classificationVsNfd": "VS – NUR FÜR DEN DIENSTGEBRAUCH"
+    "classificationVsNfd": "VS – NUR FÜR DEN DIENSTGEBRAUCH",
+    "uploadPolicy": "Datei-Uploads auf eingestufte Seiten",
+    "uploadPolicyHelp": "Anhänge erben die Einstufung der Seite, tragen selbst aber keine Kennzeichnung im Inhalt. „Blockieren\" lehnt Uploads auf eingestufte Seiten serverseitig ab.",
+    "uploadPolicyWarn": "Warnen — Upload mit deutlichem Hinweis erlauben",
+    "uploadPolicyBlock": "Blockieren — Uploads auf eingestufte Seiten ablehnen"
   },
   "landing": {
     "title": "Startseite",
diff --git a/packages/shared/i18n/en/errors.json b/packages/shared/i18n/en/errors.json
index b422c57..4d4c07c 100644
--- a/packages/shared/i18n/en/errors.json
+++ b/packages/shared/i18n/en/errors.json
@@ -110,5 +110,6 @@
   "backup_set_not_found": "The selected backup set was not found.",
   "scope_required": "This API token does not have the required scope.",
   "pond_not_found": "The pond does not exist.",
-  "classification_lower_forbidden": "You lack the permission to lower the classification (Pond Admin required)."
+  "classification_lower_forbidden": "You lack the permission to lower the classification (Pond Admin required).",
+  "classified_upload_blocked": "Uploads to classified pages are blocked on this instance."
 }
diff --git a/packages/shared/i18n/en/files.json b/packages/shared/i18n/en/files.json
index 2d33f97..c1f775d 100644
--- a/packages/shared/i18n/en/files.json
+++ b/packages/shared/i18n/en/files.json
@@ -19,5 +19,6 @@
     "svgSanitize": "Sanitize (strip scripts)",
     "svgReject": "Reject",
     "save": "Save upload settings"
-  }
+  },
+  "classifiedUploadWarning": "This page is classified “VS – NUR FÜR DEN DIENSTGEBRAUCH”. Attached files inherit the classification; the file content itself carries no marking (only the filename prefix and companion file on download)."
 }
diff --git a/packages/shared/i18n/en/settings.json b/packages/shared/i18n/en/settings.json
index ec53831..b84f7ea 100644
--- a/packages/shared/i18n/en/settings.json
+++ b/packages/shared/i18n/en/settings.json
@@ -52,7 +52,11 @@
     "newPageClassification": "Classification of new pages",
     "newPageClassificationHelp": "Default classification (VS-NfD marking) for newly created pages. The marking is not access control; separating classification levels is the environment’s job (one instance per level).",
     "classificationUnclassified": "Open — no marking",
-    "classificationVsNfd": "VS – NUR FÜR DEN DIENSTGEBRAUCH"
+    "classificationVsNfd": "VS – NUR FÜR DEN DIENSTGEBRAUCH",
+    "uploadPolicy": "File uploads to classified pages",
+    "uploadPolicyHelp": "Attachments inherit the page’s classification but carry no marking in their content. “Block” rejects uploads to classified pages server-side.",
+    "uploadPolicyWarn": "Warn — allow the upload with a clear notice",
+    "uploadPolicyBlock": "Block — reject uploads to classified pages"
   },
   "landing": {
     "title": "Landing page",