diff --git a/apps/client/src/features/share/components/share-alias-section.test.tsx b/apps/client/src/features/share/components/share-alias-section.test.tsx
index f83e00c7..deef2426 100644
--- a/apps/client/src/features/share/components/share-alias-section.test.tsx
+++ b/apps/client/src/features/share/components/share-alias-section.test.tsx
@@ -13,8 +13,7 @@ let currentAlias: IShareAlias | null = null;
 let availabilityResult: {
   valid: boolean;
   available: boolean;
-  currentPageId: string | null;
-} = { valid: true, available: true, currentPageId: null };
+} = { valid: true, available: true };
 
 vi.mock("@/features/share/queries/share-query.ts", () => ({
   useShareAliasForPageQuery: () => ({ data: currentAlias }),
@@ -56,7 +55,7 @@ describe("ShareAliasSection — taken-name handling is never a dead end", () =>
   beforeEach(() => {
     setMutateAsync.mockReset();
     currentAlias = null;
-    availabilityResult = { valid: true, available: true, currentPageId: null };
+    availabilityResult = { valid: true, available: true };
   });
 
   it("shows a 'will move it here' HINT (not a terminal error) when the name belongs to another page, and keeps Save enabled", async () => {
@@ -65,7 +64,6 @@ describe("ShareAliasSection — taken-name handling is never a dead end", () =>
     availabilityResult = {
       valid: true,
       available: false,
-      currentPageId: "page-X",
     };
 
     renderSection("page-Y");
@@ -97,7 +95,6 @@ describe("ShareAliasSection — taken-name handling is never a dead end", () =>
     availabilityResult = {
       valid: true,
       available: false,
-      currentPageId: "page-X",
     };
     // The server rejects the un-confirmed save asking the client to confirm.
     setMutateAsync.mockRejectedValueOnce({
@@ -106,7 +103,6 @@ describe("ShareAliasSection — taken-name handling is never a dead end", () =>
         status: 409,
         data: {
           code: "ALIAS_REASSIGN_REQUIRED",
-          currentPageId: "page-X",
           currentPageTitle: "Alias Test Page X",
         },
       },
diff --git a/apps/client/src/features/share/components/share-alias-section.tsx b/apps/client/src/features/share/components/share-alias-section.tsx
index a3938548..4e5cc261 100644
--- a/apps/client/src/features/share/components/share-alias-section.tsx
+++ b/apps/client/src/features/share/components/share-alias-section.tsx
@@ -48,7 +48,6 @@ export default function ShareAliasSection({
   const [availability, setAvailability] = useState<{
     valid: boolean;
     available: boolean;
-    currentPageId: string | null;
   } | null>(null);
   const [reassign, setReassign] = useState<{
     alias: string;
@@ -76,7 +75,6 @@ export default function ShareAliasSection({
         setAvailability({
           valid: res.valid,
           available: res.available,
-          currentPageId: res.currentPageId,
         });
       } catch {
         setAvailability(null);
diff --git a/apps/client/src/features/share/types/share.types.ts b/apps/client/src/features/share/types/share.types.ts
index caba0b1b..0752d12e 100644
--- a/apps/client/src/features/share/types/share.types.ts
+++ b/apps/client/src/features/share/types/share.types.ts
@@ -108,7 +108,6 @@ export interface IShareAliasAvailability {
   alias: string;
   valid: boolean;
   available: boolean;
-  currentPageId: string | null;
 }
 
 export interface ISharedPageTree {
diff --git a/apps/server/src/core/share/share-alias.service.spec.ts b/apps/server/src/core/share/share-alias.service.spec.ts
index 471ccf8e..63f16a1c 100644
--- a/apps/server/src/core/share/share-alias.service.spec.ts
+++ b/apps/server/src/core/share/share-alias.service.spec.ts
@@ -450,18 +450,22 @@ describe('ShareAliasService', () => {
         alias: 'free-name',
         valid: true,
         available: true,
-        currentPageId: null,
       });
+      // SECURITY (#495): the availability probe must NOT leak any page id.
+      expect(res).not.toHaveProperty('currentPageId');
     });
 
-    it('reports taken with the current target page', async () => {
+    it('reports taken WITHOUT leaking the current target page id (#495)', async () => {
       const { service, shareAliasRepo } = makeService();
       shareAliasRepo.findByAliasAndWorkspace.mockResolvedValue({
         id: 'a-1',
         pageId: 'p-9',
       });
       const res = await service.checkAvailability('taken', 'ws-1');
-      expect(res).toMatchObject({ available: false, currentPageId: 'p-9' });
+      expect(res).toMatchObject({ available: false });
+      // The row exists (available:false) but its pageId is never returned — an
+      // authenticated member cannot map an alias name to a page id it can't view.
+      expect(res).not.toHaveProperty('currentPageId');
     });
   });
 
diff --git a/apps/server/src/core/share/share-alias.service.ts b/apps/server/src/core/share/share-alias.service.ts
index 8b05eabb..6af94692 100644
--- a/apps/server/src/core/share/share-alias.service.ts
+++ b/apps/server/src/core/share/share-alias.service.ts
@@ -223,21 +223,28 @@ export class ShareAliasService {
     alias: string;
     valid: boolean;
     available: boolean;
-    currentPageId: string | null;
   }> {
     const alias = normalizeShareAlias(rawAlias);
     if (!isValidShareAlias(alias)) {
-      return { alias, valid: false, available: false, currentPageId: null };
+      return { alias, valid: false, available: false };
     }
     const existing = await this.shareAliasRepo.findByAliasAndWorkspace(
       alias,
       workspaceId,
     );
+    // SECURITY (#495): return ONLY the boolean availability. The previous shape
+    // leaked `currentPageId` — the id of whatever page the alias already targets —
+    // to ANY authenticated workspace member, with no view-permission check on that
+    // page. An attacker could enumerate alias names and map them to page ids they
+    // have no access to. The taken/free bit is all the "is this address free"
+    // probe needs; the reassign flow surfaces the target's title only AFTER a real
+    // setAlias attempt (the 409 ALIAS_REASSIGN_REQUIRED path), which is access-
+    // gated. If a caller ever needs the target page id, it must be returned only
+    // behind an explicit `validateCanView` on that page.
     return {
       alias,
       valid: true,
       available: !existing,
-      currentPageId: existing?.pageId ?? null,
     };
   }