diff --git a/jsonrpc/utils/src/url.ts b/jsonrpc/utils/src/url.ts
index 2ae81c41..edff28f2 100644
--- a/jsonrpc/utils/src/url.ts
+++ b/jsonrpc/utils/src/url.ts
@@ -23,5 +23,19 @@ export function isWsUrl(url: string): boolean {
 }
 
 export function isLocalhostUrl(url: string): boolean {
-  return new RegExp("wss?://localhost(:d{2,5})?").test(url);
+  // Used to relax TLS verification for local websockets only. Must match an
+  // exact loopback host — an unanchored "localhost" prefix would treat
+  // wss://localhost.evil.example as local and disable certificate checks.
+  if (!isWsUrl(url)) return false;
+  try {
+    const { hostname } = new URL(url);
+    return (
+      hostname === "localhost" ||
+      hostname === "127.0.0.1" ||
+      hostname === "[::1]" ||
+      hostname === "::1"
+    );
+  } catch {
+    return false;
+  }
 }
diff --git a/jsonrpc/utils/test/url.test.ts b/jsonrpc/utils/test/url.test.ts
new file mode 100644
index 00000000..4b37c08a
--- /dev/null
+++ b/jsonrpc/utils/test/url.test.ts
@@ -0,0 +1,27 @@
+import "mocha";
+import * as chai from "chai";
+
+import { isLocalhostUrl } from "../src/url";
+
+describe("URL", () => {
+  describe("isLocalhostUrl", () => {
+    it("accepts exact loopback websocket hosts", () => {
+      chai.expect(isLocalhostUrl("ws://localhost")).to.be.true;
+      chai.expect(isLocalhostUrl("wss://localhost:8080")).to.be.true;
+      chai.expect(isLocalhostUrl("ws://127.0.0.1:8545")).to.be.true;
+      chai.expect(isLocalhostUrl("wss://[::1]:8080")).to.be.true;
+    });
+
+    it("rejects localhost prefix lookalikes", () => {
+      chai.expect(isLocalhostUrl("wss://localhost.evil.example")).to.be.false;
+      chai.expect(isLocalhostUrl("wss://localhostfoo")).to.be.false;
+      chai.expect(isLocalhostUrl("wss://evil-localhost")).to.be.false;
+      chai.expect(isLocalhostUrl("wss://example.com")).to.be.false;
+    });
+
+    it("rejects non-websocket schemes", () => {
+      chai.expect(isLocalhostUrl("https://localhost")).to.be.false;
+      chai.expect(isLocalhostUrl("http://127.0.0.1")).to.be.false;
+    });
+  });
+});