diff --git a/extensions/browser/src/browser/proxy-files.test.ts b/extensions/browser/src/browser/proxy-files.test.ts
index 9632647ab8c4..d07dba232333 100644
--- a/extensions/browser/src/browser/proxy-files.test.ts
+++ b/extensions/browser/src/browser/proxy-files.test.ts
@@ -38,6 +38,30 @@ describe("persistBrowserProxyFiles", () => {
     await expect(fs.readFile(savedPath ?? "", "utf8")).resolves.toBe("hello from browser proxy");
   });
 
+  it("persists legitimate empty browser proxy downloads", async () => {
+    const sourcePath = "/tmp/empty-browser-download.bin";
+    const mapping = await persistBrowserProxyFiles([
+      { path: sourcePath, base64: "", mimeType: "application/octet-stream" },
+    ]);
+
+    const savedPath = mapping.get(sourcePath);
+    expect(typeof savedPath).toBe("string");
+    await expect(fs.stat(savedPath ?? "")).resolves.toMatchObject({ size: 0 });
+    await expect(fs.readFile(savedPath ?? "")).resolves.toHaveLength(0);
+  });
+
+  it.each([
+    { name: "valid unpadded base64", base64: "aGVsbG8" },
+    { name: "valid whitespace-separated base64", base64: " aG Vs bG8= \n" },
+  ])("persists $name without corrupting the download", async ({ base64 }) => {
+    const sourcePath = "/tmp/normalized-browser-download.txt";
+    const mapping = await persistBrowserProxyFiles([
+      { path: sourcePath, base64, mimeType: "text/plain" },
+    ]);
+
+    await expect(fs.readFile(mapping.get(sourcePath) ?? "", "utf8")).resolves.toBe("hello");
+  });
+
   it("persists a file at the proxy limit above the shared media default", async () => {
     const sourcePath = "/tmp/above-default.bin";
     const buffer = Buffer.alloc(BROWSER_PROXY_MAX_FILE_BYTES, 0x41);
@@ -104,6 +128,64 @@ describe("persistBrowserProxyFiles", () => {
     ).rejects.toHaveProperty("code", "ENOENT");
   });
 
+  it("rejects malformed base64 before persisting files", async () => {
+    const error = await persistBrowserProxyFiles([
+      {
+        path: "/tmp/malformed.bin",
+        base64: "aGVsbG8$",
+        mimeType: "application/octet-stream",
+      },
+    ]).then(
+      () => null,
+      (err: unknown) => err,
+    );
+    expect(error).toBeInstanceOf(Error);
+    expect((error as Error).message).toBe("browser proxy file contains malformed base64 data");
+
+    await expect(
+      fs.stat(path.join(tempHome.home, ".openclaw", "media", "browser")),
+    ).rejects.toHaveProperty("code", "ENOENT");
+  });
+
+  it.each([
+    { name: "invalid alphabet", base64: "aGVsbG8$" },
+    { name: "invalid padding", base64: "aGVsbG8===" },
+    { name: "nonzero padding bits", base64: "ZE==" },
+    { name: "impossible unpadded length", base64: "S" },
+    { name: "whitespace without encoded data", base64: " \n\t" },
+  ])("rejects $name before creating the media directory", async ({ base64 }) => {
+    await expect(
+      persistBrowserProxyFiles([
+        {
+          path: "/tmp/malformed-browser-download.bin",
+          base64,
+          mimeType: "application/octet-stream",
+        },
+      ]),
+    ).rejects.toThrow("browser proxy file contains malformed base64 data");
+
+    await expect(
+      fs.stat(path.join(tempHome.home, ".openclaw", "media", "browser")),
+    ).rejects.toHaveProperty("code", "ENOENT");
+  });
+
+  it("rejects a later malformed file without persisting an earlier valid file", async () => {
+    await expect(
+      persistBrowserProxyFiles([
+        {
+          path: "/tmp/valid-browser-download.txt",
+          base64: Buffer.from("valid browser download").toString("base64"),
+          mimeType: "text/plain",
+        },
+        { path: "/tmp/malformed-browser-download.bin", base64: "ZE==" },
+      ]),
+    ).rejects.toThrow("browser proxy file contains malformed base64 data");
+
+    await expect(
+      fs.stat(path.join(tempHome.home, ".openclaw", "media", "browser")),
+    ).rejects.toHaveProperty("code", "ENOENT");
+  });
+
   it("rejects too many files before persisting any", async () => {
     const files = Array.from({ length: BROWSER_PROXY_MAX_FILES + 1 }, (_, index) => ({
       path: `/tmp/file-${index}.bin`,
diff --git a/extensions/browser/src/browser/proxy-files.ts b/extensions/browser/src/browser/proxy-files.ts
index 3b0580f4faea..861be4282cce 100644
--- a/extensions/browser/src/browser/proxy-files.ts
+++ b/extensions/browser/src/browser/proxy-files.ts
@@ -4,6 +4,7 @@
  * Persists files returned by node-hosted browser proxy calls and rewrites
  * proxied result paths to local saved media paths.
  */
+import { canonicalizeBase64, estimateBase64DecodedBytes } from "openclaw/plugin-sdk/media-runtime";
 import {
   assertBrowserProxyFileCountWithinLimit,
   assertBrowserProxyFileBytesWithinLimits,
@@ -13,6 +14,19 @@ import {
 } from "../browser-proxy-envelope.js";
 import { saveMediaBuffer } from "../media/store.js";
 
+function decodeBrowserProxyFileBase64(file: BrowserProxyFile, totalBytes: number): Buffer {
+  const estimatedBytes = estimateBase64DecodedBytes(file.base64);
+  assertBrowserProxyFileBytesWithinLimits(estimatedBytes, totalBytes + estimatedBytes);
+  // The shared validator rejects empty input, but zero-byte downloads are valid files.
+  const canonicalBase64 = file.base64 === "" ? "" : canonicalizeBase64(file.base64);
+  if (canonicalBase64 === undefined) {
+    throw new Error("browser proxy file contains malformed base64 data");
+  }
+  const buffer = Buffer.from(canonicalBase64, "base64");
+  assertBrowserProxyFileBytesWithinLimits(buffer.byteLength, totalBytes + buffer.byteLength);
+  return buffer;
+}
+
 /** Persist proxy-returned files and return a remote-path to local-path map. */
 export async function persistBrowserProxyFiles(files: BrowserProxyFile[] | undefined) {
   if (!files || files.length === 0) {
@@ -22,9 +36,8 @@ export async function persistBrowserProxyFiles(files: BrowserProxyFile[] | undef
   const decoded: Array<{ file: BrowserProxyFile; buffer: Buffer }> = [];
   let totalBytes = 0;
   for (const file of files) {
-    const buffer = Buffer.from(file.base64, "base64");
+    const buffer = decodeBrowserProxyFileBase64(file, totalBytes);
     totalBytes += buffer.byteLength;
-    assertBrowserProxyFileBytesWithinLimits(buffer.byteLength, totalBytes);
     decoded.push({ file, buffer });
   }