diff --git a/frontend/src/app/api/[..._path]/route.ts b/frontend/src/app/api/[..._path]/route.ts
index 2ccf6ed..c4aae3a 100644
--- a/frontend/src/app/api/[..._path]/route.ts
+++ b/frontend/src/app/api/[..._path]/route.ts
@@ -6,6 +6,7 @@ import { resolveApiUrl } from "@/lib/connections/resolve";
 import { getAuthMode, usesNextAuth } from "@/types/auth-mode";
 import { generateUserJWT } from "@/lib/auth/jwt";
 import { isPrivateUrl } from "@/lib/utils/url-validation";
+import { internalErrorResponse } from "@/lib/api/error-response";
 
 function getCorsHeaders(req: NextRequest) {
   const origin = req.headers.get("origin");
@@ -156,8 +157,7 @@ async function handleRequest(req: NextRequest, method: string) {
       },
     });
   } catch (e) {
-    const error = e as Error;
-    return NextResponse.json({ error: error.message }, { status: 500 });
+    return internalErrorResponse(e, "proxy request failed");
   }
 }
 
diff --git a/frontend/src/app/api/admin/upload/route.ts b/frontend/src/app/api/admin/upload/route.ts
index b257dee..7c9aedf 100644
--- a/frontend/src/app/api/admin/upload/route.ts
+++ b/frontend/src/app/api/admin/upload/route.ts
@@ -3,6 +3,7 @@ import { auth } from "@/lib/auth";
 import { isAdmin } from "@/types/auth-mode";
 import type { UserRole } from "@/types/auth-mode";
 import { writeFile, mkdir, access, constants } from "fs/promises";
+import { internalErrorResponse } from "@/lib/api/error-response";
 import path from "path";
 
 const ALLOWED_TYPES = [
@@ -96,13 +97,7 @@ export async function POST(request: NextRequest) {
 
     return NextResponse.json({ url, filename });
   } catch (error) {
-    console.error("Upload error:", error);
-    return NextResponse.json(
-      {
-        error: `Failed to upload file: ${error instanceof Error ? error.message : "Unknown error"}`,
-      },
-      { status: 500 },
-    );
+    return internalErrorResponse(error, "admin file upload failed");
   }
 }
 
diff --git a/frontend/src/app/api/langsmith/runs/route.ts b/frontend/src/app/api/langsmith/runs/route.ts
index 148b95a..2c5908d 100644
--- a/frontend/src/app/api/langsmith/runs/route.ts
+++ b/frontend/src/app/api/langsmith/runs/route.ts
@@ -2,6 +2,7 @@ import { Client, type Run } from "langsmith";
 import { NextRequest, NextResponse } from "next/server";
 import { LangSmithRun, buildRunHierarchy } from "@/types/langsmith";
 import { usesNextAuth } from "@/types/auth-mode";
+import { internalErrorResponse } from "@/lib/api/error-response";
 
 // LangSmith Run 객체를 LangSmithRun 형식으로 변환
 function convertRun(run: Run): LangSmithRun {
@@ -137,10 +138,6 @@ export async function GET(req: NextRequest) {
 
     return NextResponse.json({ runs, hierarchy });
   } catch (error) {
-    console.error("Failed to fetch LangSmith runs:", error);
-    return NextResponse.json(
-      { error: error instanceof Error ? error.message : "Unknown error" },
-      { status: 500 },
-    );
+    return internalErrorResponse(error, "LangSmith runs fetch failed");
   }
 }
diff --git a/frontend/src/app/api/upload/route.ts b/frontend/src/app/api/upload/route.ts
index 6ce07c3..fbff943 100644
--- a/frontend/src/app/api/upload/route.ts
+++ b/frontend/src/app/api/upload/route.ts
@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { auth } from "@/lib/auth";
 import { usesNextAuth } from "@/types/auth-mode";
 import { getSetting } from "@/lib/services/settings.service";
+import { internalErrorResponse } from "@/lib/api/error-response";
 import { writeFile, mkdir, access, constants } from "fs/promises";
 import path from "path";
 
@@ -106,13 +107,7 @@ export async function POST(request: NextRequest) {
 
     return NextResponse.json({ url, filename });
   } catch (error) {
-    console.error("Upload error:", error);
-    return NextResponse.json(
-      {
-        error: `Failed to upload file: ${error instanceof Error ? error.message : "Unknown error"}`,
-      },
-      { status: 500 },
-    );
+    return internalErrorResponse(error, "user file upload failed");
   }
 }
 
diff --git a/frontend/src/lib/api/error-response.ts b/frontend/src/lib/api/error-response.ts
new file mode 100644
index 0000000..cbd8abe
--- /dev/null
+++ b/frontend/src/lib/api/error-response.ts
@@ -0,0 +1,14 @@
+import { NextResponse } from "next/server";
+
+/**
+ * Return a generic 500 JSON response while logging the real error server-side.
+ * Prevents leaking internal hostnames, ports, file-system paths, or API keys
+ * to clients (OWASP A05:2021 — Security Misconfiguration).
+ */
+export function internalErrorResponse(error: unknown, context: string) {
+  console.error(`[api] ${context}`, error);
+  return NextResponse.json(
+    { error: "Internal server error" },
+    { status: 500 },
+  );
+}