diff --git a/api/server/routes/tags.js b/api/server/routes/tags.js
index 10be2b2e8f..d4584a5212 100644
--- a/api/server/routes/tags.js
+++ b/api/server/routes/tags.js
@@ -98,7 +98,8 @@ router.put('/:tag', configMiddleware, async (req, res) => {
     const decodedTag = decodeURIComponent(req.params.tag);
     const tag = await updateConversationTag(req.user.id, decodedTag, req.body);
     if (tag) {
-      await enforceForcedRetentionForTag(req, req.body?.tag || decodedTag, 'PUT /api/tags/:tag');
+      const renamedTag = typeof req.body?.tag === 'string' ? req.body.tag : decodedTag;
+      await enforceForcedRetentionForTag(req, renamedTag, 'PUT /api/tags/:tag');
       res.status(200).json(tag);
     } else {
       res.status(404).json({ error: 'Tag not found' });
diff --git a/packages/data-schemas/src/methods/message.spec.ts b/packages/data-schemas/src/methods/message.spec.ts
index f69b47a742..cda4ff692a 100644
--- a/packages/data-schemas/src/methods/message.spec.ts
+++ b/packages/data-schemas/src/methods/message.spec.ts
@@ -1244,6 +1244,29 @@ describe('Message Operations', () => {
       const convo = await Conversation().findOne({ conversationId }).lean();
       expect(convo?.expiredAt ?? null).toBeNull();
     });
+
+    it('ignores a non-string tag instead of matching every conversation (NoSQL injection)', async () => {
+      const conversationId = uuidv4();
+      await Conversation().create({
+        conversationId,
+        user: 'user123',
+        endpoint: 'openAI',
+        tags: ['work'],
+      });
+
+      await applyForcedRetentionToTag(
+        {
+          userId: 'user123',
+          interfaceConfig: { temporaryChatRetention: 24, retentionMode: RetentionMode.EPHEMERAL },
+        },
+        { tag: { $gt: '' } as unknown as string },
+        { context: 'PUT /api/tags/:tag' },
+      );
+
+      const convo = await Conversation().findOne({ conversationId }).lean();
+      expect(convo?.isTemporary ?? null).not.toBe(true);
+      expect(convo?.expiredAt ?? null).toBeNull();
+    });
   });
 
   describe('Message cursor pagination', () => {
diff --git a/packages/data-schemas/src/methods/message.ts b/packages/data-schemas/src/methods/message.ts
index 133b4cbcae..d40267e5f1 100644
--- a/packages/data-schemas/src/methods/message.ts
+++ b/packages/data-schemas/src/methods/message.ts
@@ -384,6 +384,12 @@ export function createMessageMethods(mongoose: typeof import('mongoose')): Messa
     if (!isForcedTemporaryRetention(interfaceConfig?.retentionMode)) {
       return;
     }
+    if (typeof conversationId !== 'string' || conversationId.length === 0) {
+      logger.warn(
+        `[applyForcedRetention] Ignoring non-string conversationId (context: ${metadata?.context ?? 'n/a'})`,
+      );
+      return;
+    }
 
     let forcedExpiredAt: Date;
     try {
@@ -409,7 +415,7 @@ export function createMessageMethods(mongoose: typeof import('mongoose')): Messa
       );
     }
 
-    if (messageId) {
+    if (typeof messageId === 'string' && messageId.length > 0) {
       await Message.updateOne(
         { messageId, user: userId },
         { $set: { isTemporary: true, expiredAt: forcedExpiredAt } },
@@ -440,6 +446,12 @@ export function createMessageMethods(mongoose: typeof import('mongoose')): Messa
     if (!isForcedTemporaryRetention(interfaceConfig?.retentionMode)) {
       return;
     }
+    if (typeof tag !== 'string' || tag.length === 0) {
+      logger.warn(
+        `[applyForcedRetentionToTag] Ignoring non-string tag (context: ${metadata?.context ?? 'n/a'})`,
+      );
+      return;
+    }
 
     let forcedExpiredAt: Date;
     try {