diff --git a/app/controllers/versioninfocontroller.js b/app/controllers/versioninfocontroller.js
index 0d41048..b904053 100644
--- a/app/controllers/versioninfocontroller.js
+++ b/app/controllers/versioninfocontroller.js
@@ -33,6 +33,37 @@ async function requireMaster(authKey, res) {
     return true;
 }
 
+/**
+ * Reject reads whose authKey header is missing OR present-but-unknown.
+ *
+ * VersionInfo reads were originally gated purely on "header present"
+ * — `getById` and `list` accepted any non-empty string in `authKey`
+ * and returned 200. The README's endpoint table says "yes (authKey)"
+ * for these endpoints, which the rest of the codebase consistently
+ * treats as "any VALID authKey, master or scoped"; a literal
+ * presence-check breaks that contract.
+ *
+ * attachAuth (mounted at /v1/*) has already populated req.isMaster
+ * and req.companyId from the supplied header, so this helper just
+ * reads the resolved state without a second DB round-trip.
+ *
+ * Master keys pass (isMaster=true, companyId=-1 by convention).
+ * Non-master keys pass when they resolved to a real company. An
+ * unknown header is the case we want to reject — !isMaster AND
+ * companyId===-1.
+ */
+function requireValidAuth(req, res) {
+    if (!req.authKey) {
+        res.status(403).json({ message: "Authorization key not sent." });
+        return false;
+    }
+    if (!req.isMaster && req.companyId === -1) {
+        res.status(403).json({ message: "Invalid Authorization Key." });
+        return false;
+    }
+    return true;
+}
+
 exports.create = async (req, res) => {
     const authKey = req.get('authKey');
     if (!(await requireMaster(authKey, res))) return;
@@ -52,10 +83,7 @@ exports.create = async (req, res) => {
 };
 
 exports.getById = async (req, res) => {
-    const authKey = req.get('authKey');
-    if (!authKey) {
-        return res.status(403).json({ message: "Authorization key not sent." });
-    }
+    if (!requireValidAuth(req, res)) return;
     try {
         const v = await VersionInfo.findByPk(req.params.id);
         if (!v) return res.status(404).json({ message: "Not found." });
@@ -67,10 +95,7 @@ exports.getById = async (req, res) => {
 };
 
 exports.list = async (req, res) => {
-    const authKey = req.get('authKey');
-    if (!authKey) {
-        return res.status(403).json({ message: "Authorization key not sent." });
-    }
+    if (!requireValidAuth(req, res)) return;
 
     const requestedLimit = parseInt(req.query.limit, 10);
     const limit = Number.isInteger(requestedLimit) && requestedLimit > 0
diff --git a/tests/api/versioninfo.test.js b/tests/api/versioninfo.test.js
index 4378976..43dc02d 100644
--- a/tests/api/versioninfo.test.js
+++ b/tests/api/versioninfo.test.js
@@ -49,6 +49,22 @@ describe('VersionInfo auth contract', () => {
     test('DELETE 403 for non-master key', async () => {
         expect((await request(app).delete('/v1/versioninfo/1').set('authKey', 'not-master')).status).toBe(403);
     });
+
+    test('GET 403 for unknown authKey (header present but not in DB)', async () => {
+        // VersionInfo reads previously gated only on header-present, so any
+        // non-empty string in `authKey` returned 200. The README's endpoint
+        // table says "yes (authKey)" for reads, which the rest of the API
+        // consistently means "any VALID authKey". Pin the tightening so a
+        // future refactor can't accidentally drop the validation check.
+        const res = await request(app).get('/v1/versioninfo/1').set('authKey', 'unknown');
+        expect(res.status).toBe(403);
+        expect(res.body.message).toMatch(/Invalid Authorization Key/i);
+    });
+    test('GET list 403 for unknown authKey', async () => {
+        const res = await request(app).get('/v1/versioninfo').set('authKey', 'unknown');
+        expect(res.status).toBe(403);
+        expect(res.body.message).toMatch(/Invalid Authorization Key/i);
+    });
 });
 
 describe('VersionInfo route mounting', () => {