diff --git a/apps/web/src/__tests__/safe-redirect.test.ts b/apps/web/src/__tests__/safe-redirect.test.ts
new file mode 100644
index 0000000..d20a8be
--- /dev/null
+++ b/apps/web/src/__tests__/safe-redirect.test.ts
@@ -0,0 +1,24 @@
+import { describe, expect, it } from "vitest";
+import { safeRedirectPath } from "@/lib/safe-redirect";
+
+describe("safeRedirectPath", () => {
+  it("preserves internal paths, queries, and fragments", () => {
+    expect(safeRedirectPath("/usage?range=30d#details")).toBe(
+      "/usage?range=30d#details"
+    );
+  });
+
+  it.each([
+    "https://attacker.example/phish",
+    "//attacker.example/phish",
+    "/\\attacker.example/phish",
+    "javascript:alert(1)",
+    "account",
+  ])("rejects unsafe redirect %s", (value) => {
+    expect(safeRedirectPath(value)).toBe("/account");
+  });
+
+  it("uses the requested fallback for missing values", () => {
+    expect(safeRedirectPath(null, "/")).toBe("/");
+  });
+});
diff --git a/apps/web/src/app/api/auth/callback/route.ts b/apps/web/src/app/api/auth/callback/route.ts
index 24ffcf6..cc1dbba 100644
--- a/apps/web/src/app/api/auth/callback/route.ts
+++ b/apps/web/src/app/api/auth/callback/route.ts
@@ -1,5 +1,6 @@
 import { NextRequest, NextResponse } from "next/server";
 import { createClient } from "@supabase/supabase-js";
+import { safeRedirectPath } from "@/lib/safe-redirect";
 
 const SUPABASE_URL = process.env.NEXT_PUBLIC_SUPABASE_URL;
 const SUPABASE_SERVICE_KEY = process.env.SUPABASE_SERVICE_ROLE_KEY;
@@ -26,8 +27,7 @@ export async function GET(request: NextRequest) {
   const { searchParams } = new URL(request.url);
   const code = searchParams.get("code");
   const ref = searchParams.get("ref") || "";
-  const nextParam = searchParams.get("next") || "/account";
-  const nextPath = nextParam.startsWith("/") ? nextParam : "/account";
+  const nextPath = safeRedirectPath(searchParams.get("next"));
 
   if (!code) {
     return NextResponse.redirect(`${APP_URL}/auth/login?error=no_code`);
diff --git a/apps/web/src/app/auth/login/page.tsx b/apps/web/src/app/auth/login/page.tsx
index f878fd8..1b656a0 100644
--- a/apps/web/src/app/auth/login/page.tsx
+++ b/apps/web/src/app/auth/login/page.tsx
@@ -3,6 +3,7 @@
 import { useMemo, useState } from "react";
 import Link from "next/link";
 import { setAccessToken } from "@/lib/auth-client";
+import { safeRedirectPath } from "@/lib/safe-redirect";
 
 export default function LoginPage() {
   const [email, setEmail] = useState("");
@@ -11,8 +12,7 @@ export default function LoginPage() {
   const [error, setError] = useState("");
   const nextPath = useMemo(() => {
     if (typeof window === "undefined") return "/account";
-    const raw = new URLSearchParams(window.location.search).get("next") || "/account";
-    return raw.startsWith("/") ? raw : "/account";
+    return safeRedirectPath(new URLSearchParams(window.location.search).get("next"));
   }, []);
 
   const handleSubmit = async (e: React.FormEvent) => {
diff --git a/apps/web/src/app/auth/signup/page.tsx b/apps/web/src/app/auth/signup/page.tsx
index 13877cc..3a9305e 100644
--- a/apps/web/src/app/auth/signup/page.tsx
+++ b/apps/web/src/app/auth/signup/page.tsx
@@ -2,6 +2,7 @@
 
 import { useState, useEffect, useMemo } from "react";
 import Link from "next/link";
+import { safeRedirectPath } from "@/lib/safe-redirect";
 
 export default function SignupPage() {
   const [email, setEmail] = useState("");
@@ -14,8 +15,7 @@ export default function SignupPage() {
   const [success, setSuccess] = useState(false);
   const nextPath = useMemo(() => {
     if (typeof window === "undefined") return "/account";
-    const raw = new URLSearchParams(window.location.search).get("next") || "/account";
-    return raw.startsWith("/") ? raw : "/account";
+    return safeRedirectPath(new URLSearchParams(window.location.search).get("next"));
   }, []);
 
   useEffect(() => {
diff --git a/apps/web/src/lib/safe-redirect.ts b/apps/web/src/lib/safe-redirect.ts
new file mode 100644
index 0000000..4efc1c3
--- /dev/null
+++ b/apps/web/src/lib/safe-redirect.ts
@@ -0,0 +1,16 @@
+const REDIRECT_BASE = "https://threatcrush.invalid";
+
+export function safeRedirectPath(
+  value: string | null | undefined,
+  fallback = "/account"
+): string {
+  if (!value || !value.startsWith("/")) return fallback;
+
+  try {
+    const url = new URL(value, REDIRECT_BASE);
+    if (url.origin !== REDIRECT_BASE) return fallback;
+    return `${url.pathname}${url.search}${url.hash}`;
+  } catch {
+    return fallback;
+  }
+}