diff --git a/config/quality/eslint-suppressions.json b/config/quality/eslint-suppressions.json
index e76889cf4d4..f6c6da6a620 100644
--- a/config/quality/eslint-suppressions.json
+++ b/config/quality/eslint-suppressions.json
@@ -1651,11 +1651,6 @@
       "count": 1
     }
   },
-  "src/lib/telegram/initData.ts": {
-    "@typescript-eslint/no-unused-vars": {
-      "count": 1
-    }
-  },
   "src/lib/usage/apiKeySelfService.ts": {
     "no-restricted-syntax": {
       "count": 1
diff --git a/src/lib/telegram/initData.ts b/src/lib/telegram/initData.ts
index 479d9063da9..43c696546dd 100644
--- a/src/lib/telegram/initData.ts
+++ b/src/lib/telegram/initData.ts
@@ -12,7 +12,7 @@
  * directly unit-testable. Never trust the client-side `initData` alone —
  * verification MUST happen server-side.
  */
-import { createHash, createHmac, timingSafeEqual } from "node:crypto";
+import { createHmac, timingSafeEqual } from "node:crypto";
 
 /** Parse a URLSearchParams-style initData string into a record. */
 export function parseInitData(initData: string): Record<string, string> {
@@ -21,8 +21,17 @@ export function parseInitData(initData: string): Record<string, string> {
   for (const pair of initData.split("&")) {
     const eq = pair.indexOf("=");
     if (eq <= 0) continue;
-    const key = decodeURIComponent(pair.slice(0, eq));
-    const value = decodeURIComponent(pair.slice(eq + 1));
+    let key: string;
+    let value: string;
+    try {
+      key = decodeURIComponent(pair.slice(0, eq));
+      value = decodeURIComponent(pair.slice(eq + 1));
+    } catch {
+      // A malformed percent escape is not a valid initData field. Skip the pair
+      // so the caller gets a signature mismatch (401) instead of an uncaught
+      // URIError (500).
+      continue;
+    }
     if (key && !(key in out)) out[key] = value;
   }
   return out;
diff --git a/tests/unit/telegram-init-data.test.ts b/tests/unit/telegram-init-data.test.ts
index d755acba6a7..730399d07f6 100644
--- a/tests/unit/telegram-init-data.test.ts
+++ b/tests/unit/telegram-init-data.test.ts
@@ -71,3 +71,10 @@ test("verifyInitData handles chunked/encoded keys", () => {
   });
   assert.equal(verifyInitData(initData, BOT_TOKEN), true);
 });
+
+test("verifyInitData returns false on a malformed percent escape instead of throwing", () => {
+  assert.equal(verifyInitData("user=%ZZ&hash=abc", BOT_TOKEN), false);
+  const parsed = parseInitData("user=%ZZ&hash=abc");
+  assert.equal(parsed.user, undefined);
+  assert.equal(parsed.hash, "abc");
+});