diff --git a/.changeset/kind-rooms-report.md b/.changeset/kind-rooms-report.md
new file mode 100644
index 00000000000..93e8ed53361
--- /dev/null
+++ b/.changeset/kind-rooms-report.md
@@ -0,0 +1,9 @@
+---
+'@clerk/backend': patch
+---
+
+Fix `URIError: URI malformed` being thrown while parsing the `Cookie` header.
+
+`ClerkRequest` decodes percent-escapes across the whole header rather than per value, so an invalid sequence in any cookie — including ones Clerk neither set nor reads, such as those written by analytics or third-party scripts — reached `decodeURIComponent` and threw. The decode runs from the constructor, so the error escaped `createClerkRequest` and failed the request before any auth logic ran. Because the offending value stays in the browser until it expires, every subsequent request from that client failed too.
+
+Escape sequences that cannot be decoded are now left as their raw text, and the rest of the header parses as before.
diff --git a/packages/backend/src/tokens/__tests__/clerkRequest.test.ts b/packages/backend/src/tokens/__tests__/clerkRequest.test.ts
index 1b75b88cd44..ec23ceda72d 100644
--- a/packages/backend/src/tokens/__tests__/clerkRequest.test.ts
+++ b/packages/backend/src/tokens/__tests__/clerkRequest.test.ts
@@ -97,6 +97,30 @@ describe('createClerkRequest', () => {
       expect(req.cookies.get('baz')).toBe('qux');
     });
 
+    // `%E2` is an incomplete UTF-8 lead byte, so `decodeURIComponent` throws on it.
+    // The decode runs over the whole header, so a cookie Clerk never set and never
+    // reads can fail the request before any auth logic runs (issue #9333).
+    it('does not throw when another cookie has a malformed percent-escape', () => {
+      const req = new Request('http://localhost:3000', {
+        headers: new Headers({ cookie: '__session=abc; analytics_id=%E2%9' }),
+      });
+      expect(() => createClerkRequest(req)).not.toThrow();
+      expect(createClerkRequest(req).cookies.get('__session')).toBe('abc');
+    });
+
+    // A value that cannot be decoded is kept as-is, so callers still see whatever
+    // the client sent rather than an empty or dropped cookie.
+    it.each([
+      ['truncated sequence', '%E2%9'],
+      ['lone continuation byte', '%98'],
+      ['overlong encoding', '%C0%80'],
+    ])('leaves a cookie with a %s undecoded', (_label, value) => {
+      const req = createClerkRequest(
+        new Request('http://localhost:3000', { headers: new Headers({ cookie: `analytics_id=${value}` }) }),
+      );
+      expect(req.cookies.get('analytics_id')).toBe(value);
+    });
+
     it('should parse and return cookies even if no cookie header exists', () => {
       const req = createClerkRequest(new Request('http://localhost:3000', { headers: new Headers() }));
       expect(req.cookies.get('foo')).toBeUndefined();
diff --git a/packages/backend/src/tokens/clerkRequest.ts b/packages/backend/src/tokens/clerkRequest.ts
index 8b02266c643..54163f13aff 100644
--- a/packages/backend/src/tokens/clerkRequest.ts
+++ b/packages/backend/src/tokens/clerkRequest.ts
@@ -99,7 +99,22 @@ class ClerkRequest extends Request {
   }
 
   private decodeCookieValue(str: string) {
-    return str ? str.replace(/(%[0-9A-Z]{2})+/g, decodeURIComponent) : str;
+    if (!str) {
+      return str;
+    }
+
+    // The decode runs over the whole header rather than per value, so an escape
+    // in any cookie - including ones Clerk neither set nor reads - reaches
+    // `decodeURIComponent`, which throws on invalid UTF-8 (truncated, lone, or
+    // overlong sequences). This is called from the constructor, so that would
+    // fail the request before any auth logic runs. Leave such runs raw instead.
+    return str.replace(/(%[0-9A-Z]{2})+/g, match => {
+      try {
+        return decodeURIComponent(match);
+      } catch {
+        return match;
+      }
+    });
   }
 }