diff --git a/lib/utils/resolve-file-proxy.ts b/lib/utils/resolve-file-proxy.ts
index 3145b4e..5743f4d 100644
--- a/lib/utils/resolve-file-proxy.ts
+++ b/lib/utils/resolve-file-proxy.ts
@@ -1,6 +1,6 @@
 import type { FileProxy } from "../db/schema"
 import { readFile } from "node:fs/promises"
-import { join } from "node:path"
+import { relative, resolve, sep } from "node:path"
 import { normalizePath } from "./normalize-path"
 
 export async function resolveFileProxy(
@@ -26,7 +26,13 @@ async function resolveDiskProxy(
   diskPath: string,
   relativePath: string,
 ): Promise<Response> {
-  const fullPath = join(diskPath, relativePath)
+  const rootPath = resolve(diskPath)
+  const fullPath = resolve(rootPath, relativePath)
+  const pathFromRoot = relative(rootPath, fullPath)
+
+  if (pathFromRoot === ".." || pathFromRoot.startsWith(`..${sep}`)) {
+    return new Response("File not found", { status: 404 })
+  }
 
   try {
     const content = await readFile(fullPath)
diff --git a/tests/routes/file-proxy02.test.ts b/tests/routes/file-proxy02.test.ts
index c1314e8..2aba85f 100644
--- a/tests/routes/file-proxy02.test.ts
+++ b/tests/routes/file-proxy02.test.ts
@@ -91,6 +91,42 @@ test("disk proxy with query param download", async () => {
   }
 })
 
+test("disk proxy blocks parent directory traversal", async () => {
+  const { axios } = await getTestServer()
+
+  const tempDir = await mkdtemp(join(tmpdir(), "file-proxy-traversal-"))
+  const proxyRoot = join(tempDir, "root")
+
+  try {
+    await mkdir(proxyRoot)
+    await writeFile(join(proxyRoot, "safe.txt"), "Safe proxy content")
+    await writeFile(join(tempDir, "secret.txt"), "Secret sibling content")
+
+    await axios.post("/file_proxies/create", {
+      proxy_type: "disk",
+      disk_path: proxyRoot,
+      matching_pattern: "traversal/*",
+    })
+
+    const safeRes = await axios.get("/files/download", {
+      params: { file_path: "/traversal/safe.txt" },
+    })
+    expect(safeRes.status).toBe(200)
+    expect(safeRes.data).toBe("Safe proxy content")
+
+    await expect(
+      axios.get("/files/download", {
+        params: { file_path: "/traversal/../secret.txt" },
+      }),
+    ).rejects.toMatchObject({
+      status: 404,
+      data: "File not found",
+    })
+  } finally {
+    await rm(tempDir, { recursive: true, force: true })
+  }
+})
+
 test("disk proxy binary file", async () => {
   const { axios } = await getTestServer()