diff --git a/src/features/auth/helpers/return-to.helper.spec.ts b/src/features/auth/helpers/return-to.helper.spec.ts
new file mode 100644
index 00000000..af8a79bc
--- /dev/null
+++ b/src/features/auth/helpers/return-to.helper.spec.ts
@@ -0,0 +1,40 @@
+import { resolveReturnTo } from '@/features/auth/helpers/return-to.helper';
+
+const FALLBACK = 'https://caquick.site';
+const ALLOWED = ['https://caquick.site', 'http://localhost:3000'];
+
+describe('resolveReturnTo', () => {
+  it.each([
+    ['https://caquick.site/mypage', 'https://caquick.site/mypage'],
+    ['http://localhost:3000/a?b=1', 'http://localhost:3000/a?b=1'],
+    ['  https://caquick.site/x  ', 'https://caquick.site/x'],
+  ])('허용 오리진이면 그 주소로 보낸다: %s', (raw, expected) => {
+    expect(resolveReturnTo(raw, FALLBACK, ALLOWED)).toBe(expected);
+  });
+
+  it.each([
+    ['접두가 같은 다른 호스트', 'https://caquick.site.evil.com/x'],
+    ['userinfo로 위장한 호스트', 'https://caquick.site@evil.com/x'],
+    ['이어 붙인 호스트', 'https://caquick.siteevil.com'],
+    ['스킴 불일치', 'http://caquick.site/x'],
+    ['포트 불일치', 'http://localhost:3001/x'],
+    ['스킴 상대 주소', '//evil.com'],
+    ['상대 경로', '/mypage'],
+    ['javascript 스킴', 'javascript:alert(1)'],
+    ['빈 문자열', ''],
+    ['공백', '   '],
+    ['undefined', undefined],
+  ])('%s(%s)는 기본 주소로 보낸다', (_label, raw) => {
+    expect(resolveReturnTo(raw, FALLBACK, ALLOWED)).toBe(FALLBACK);
+  });
+
+  it('기본 주소의 오리진은 허용 목록에 없어도 허용한다', () => {
+    expect(
+      resolveReturnTo(
+        'https://front.example/a',
+        'https://front.example',
+        ALLOWED,
+      ),
+    ).toBe('https://front.example/a');
+  });
+});
diff --git a/src/features/auth/helpers/return-to.helper.ts b/src/features/auth/helpers/return-to.helper.ts
new file mode 100644
index 00000000..422b2bcc
--- /dev/null
+++ b/src/features/auth/helpers/return-to.helper.ts
@@ -0,0 +1,24 @@
+/**
+ * 로그인 뒤 돌아갈 주소. 접두 비교는 `https://caquick.site.evil.com`·`https://caquick.site@evil.com`을 통과시키므로
+ * URL로 파싱해 오리진이 정확히 같을 때만 허용하고, 아니면 기본 프론트 주소로 보낸다.
+ */
+export function resolveReturnTo(
+  raw: string | undefined,
+  fallback: string,
+  allowed: readonly string[],
+): string {
+  const url = parseHttpUrl(raw?.trim() ?? '');
+  if (!url) return fallback;
+
+  const origins = [fallback, ...allowed].map((u) => parseHttpUrl(u)?.origin);
+  return origins.includes(url.origin) ? url.href : fallback;
+}
+
+function parseHttpUrl(raw: string): URL | null {
+  try {
+    const url = new URL(raw);
+    return url.protocol === 'https:' || url.protocol === 'http:' ? url : null;
+  } catch {
+    return null;
+  }
+}
diff --git a/src/features/auth/services/oidc-login.service.ts b/src/features/auth/services/oidc-login.service.ts
index 53bd0ec5..30c51a1c 100644
--- a/src/features/auth/services/oidc-login.service.ts
+++ b/src/features/auth/services/oidc-login.service.ts
@@ -7,6 +7,7 @@ import type { AuthConfig } from '@/config/auth.config';
 import { ALLOWED_RETURN_TO_DOMAINS } from '@/features/auth/constants/auth.constants';
 import { AuthCookieOptions } from '@/features/auth/helpers/auth-cookie-options.helper';
 import { AuthCookie } from '@/features/auth/helpers/auth-cookie.helper';
+import { resolveReturnTo } from '@/features/auth/helpers/return-to.helper';
 import {
   ACCOUNT_REPOSITORY,
   type IAccountRepository,
@@ -202,12 +203,7 @@ export class OidcLoginService {
   /** 오픈 리다이렉트 방지. */
   private normalizeReturnTo(raw: string | undefined): string {
     const frontend = this.config.getOrThrow<AuthConfig>('auth').frontendBaseUrl;
-
-    if (!raw || raw.trim().length === 0) return frontend;
-
-    const allowed = [frontend, ...ALLOWED_RETURN_TO_DOMAINS];
-    const ok = allowed.some((prefix) => raw.startsWith(prefix));
-    return ok ? raw : frontend;
+    return resolveReturnTo(raw, frontend, ALLOWED_RETURN_TO_DOMAINS);
   }
 
   private pickCallbackParams(req: Request): Record<string, string | string[]> {