diff --git a/CHANGELOG.md b/CHANGELOG.md
index 470f14e..f7211ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@
 
 - Hardened incoming RSS/Atom sources with public-HTTPS validation, redirect checks, response-size limits, and safe XML declaration rejection.
 
+### Fixed
+
+- Tightened standard webhook signature validation to reject invalid timestamps and non-v1 signature schemes.
+
 ## [0.7.0] - 2026-07-19
 
 ### Fixed
diff --git a/lib/webhook.ts b/lib/webhook.ts
index eb7fd30..6c315fb 100644
--- a/lib/webhook.ts
+++ b/lib/webhook.ts
@@ -9,7 +9,7 @@ export function webhookSecretMatches(secret: string, expectedHash: string | null
   return actual.length === expected.length && timingSafeEqual(actual, expected);
 }
 export function standardWebhookMatches(secret: string, id: string | null, timestamp: string | null, signature: string | null, body: string) {
-  if (!id || !timestamp || !signature || Math.abs(Date.now() / 1000 - Number(timestamp)) > 300) return false;
+  const seconds = Number(timestamp); if (!id || !timestamp || !signature || !Number.isFinite(seconds) || !Number.isInteger(seconds) || Math.abs(Date.now() / 1000 - seconds) > 300) return false;
   const expected = createHmac("sha256", secret).update(`${id}.${timestamp}.${body}`).digest("base64");
-  return signature.split(" ").some((item) => { const value = item.split(",")[1]; if (!value) return false; const actual = Buffer.from(value); const target = Buffer.from(expected); return actual.length === target.length && timingSafeEqual(actual, target); });
+  return signature.split(" ").some((item) => { const [version, value] = item.split(","); if (version !== "v1" || !value) return false; const actual = Buffer.from(value); const target = Buffer.from(expected); return actual.length === target.length && timingSafeEqual(actual, target); });
 }
diff --git a/tests/webhook.test.ts b/tests/webhook.test.ts
new file mode 100644
index 0000000..4ffa6da
--- /dev/null
+++ b/tests/webhook.test.ts
@@ -0,0 +1,18 @@
+import assert from "node:assert/strict";
+import { createHmac } from "node:crypto";
+import { test } from "node:test";
+import { standardWebhookMatches, webhookSecretHash, webhookSecretMatches } from "../lib/webhook";
+
+test("verifies path secrets using a constant-time hash comparison", () => {
+  const secret = "path-secret"; assert.equal(webhookSecretMatches(secret, webhookSecretHash(secret)), true); assert.equal(webhookSecretMatches("wrong", webhookSecretHash(secret)), false); assert.equal(webhookSecretMatches(secret, null), false);
+});
+
+test("accepts only fresh v1 standard webhooks with an exact body signature", () => {
+  const secret = "signing-secret", id = "event-1", timestamp = String(Math.floor(Date.now() / 1000)), body = '{"type":"memo.updated"}';
+  const signature = createHmac("sha256", secret).update(`${id}.${timestamp}.${body}`).digest("base64");
+  assert.equal(standardWebhookMatches(secret, id, timestamp, `v1,${signature}`, body), true);
+  assert.equal(standardWebhookMatches(secret, id, timestamp, `v1,${signature}`, "{}"), false);
+  assert.equal(standardWebhookMatches(secret, id, "not-a-time", `v1,${signature}`, body), false);
+  assert.equal(standardWebhookMatches(secret, id, timestamp, `v2,${signature}`, body), false);
+  assert.equal(standardWebhookMatches(secret, id, String(Math.floor(Date.now() / 1000) - 301), `v1,${signature}`, body), false);
+});