fix(ssrf): block the full IPv6 link-local range

src/local-guard.test.ts

@@ -41,13 +41,29 @@ describe("isBlockedSsrfHost", () => {
       "2002:7f00:1::",
       "64:ff9b::7f00:1",
       "fd00::1",
+      "fe80::1",
     ]) {
       expect(isBlockedSsrfHost(h), h).toBe(true);
     }
   });
 
+  it("blocks the whole fe80::/10 link-local range, not only the fe80:: prefix", () => {
+    for (const h of ["fe81::1", "fe9f::1", "fea0::1", "febf::1", "[febf::1]", "FE81::ABCD"]) {
+      expect(isBlockedSsrfHost(h), h).toBe(true);
+    }
+  });
+
   it("allows public hosts", () => {
-    for (const h of ["example.com", "8.8.8.8", "fda.gov", "blockrun.ai"]) {
+    for (const h of [
+      "example.com",
+      "8.8.8.8",
+      "fda.gov",
+      "blockrun.ai",
+      "fe7f::1",
+      "fe8::1",
+      "fec0::1",
+      "2001:4860:4860::8888",
+    ]) {
       expect(isBlockedSsrfHost(h), h).toBe(false);
     }
   });
@@ -100,6 +116,15 @@ describe("resolvePublicAddresses", () => {
     ]);
   });
 
+  it("refuses a link-local IPv6 literal outside the fe80:: prefix", async () => {
+    const resolve = async () => {
+      throw new Error("resolver called");
+    };
+    await expect(resolvePublicAddresses("[fe81::1]", resolve)).rejects.toThrow(
+      /private\/loopback\/metadata/,
+    );
+  });
+
   it("refuses a name that resolves to nothing", async () => {
     await expect(resolvePublicAddresses("void.example", dnsOf({}))).rejects.toThrow(
       /could not resolve/,

src/local-guard.ts

@@ -89,6 +89,18 @@ function v4FromHex(hi: number, lo: number): string {
   return `${(hi >>> 8) & 255}.${hi & 255}.${(lo >>> 8) & 255}.${lo & 255}`;
 }
 
+/**
+ * fe80::/10 (RFC 4291). Link-local is fe80:: through febf::, not only the
+ * fe80:: prefix. The first hextet carries those 10 bits, so fe81::1 is
+ * link-local while fe8::1 (hextet 0x0fe8) is not.
+ */
+function isIpv6LinkLocal(address: string): boolean {
+  const first = address.split(":")[0];
+  if (!/^[0-9a-f]{1,4}$/.test(first)) return false;
+  const value = parseInt(first, 16);
+  return value >= 0xfe80 && value <= 0xfebf;
+}
+
 /**
  * True for loopback, private, link-local, CGNAT and cloud-metadata hosts,
  * including the IPv6 forms that embed an IPv4 address. Literal-host based:
@@ -104,7 +116,7 @@ export function isBlockedSsrfHost(hostname: string): boolean {
 
   if (h.includes(":")) {
     if (h === "::1" || h === "::") return true;
-    if (h.startsWith("fe80:") || h.startsWith("fc") || h.startsWith("fd")) return true;
+    if (isIpv6LinkLocal(h) || h.startsWith("fc") || h.startsWith("fd")) return true;
     // 6to4: 2002:WWXX:YYZZ::/16 embeds W.X.Y.Z.
     const sixToFour = h.match(/^2002:([0-9a-f]{1,4}):([0-9a-f]{1,4}):/);
     if (sixToFour) {