diff --git a/CHANGELOG.md b/CHANGELOG.md
index d5d3087921..887be686e4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Agents: enforce sandbox validation for message media/file paths. (#6398) Thanks @leszekszpunar.
 - Docs: run oxfmt to fix format checks. (#6513) Thanks @app/clawdinator.
 - Auto-reply: avoid referencing workspace files in /new greeting prompt. (#5706) Thanks @bravostation.
 - Process: resolve Windows `spawn()` failures for npm-family CLIs by appending `.cmd` when needed. (#5815) Thanks @thejhinvirtuoso.
diff --git a/src/agents/tools/message-tool.test.ts b/src/agents/tools/message-tool.test.ts
index 15d416fd89..2d3ecb7bae 100644
--- a/src/agents/tools/message-tool.test.ts
+++ b/src/agents/tools/message-tool.test.ts
@@ -187,6 +187,27 @@ describe("message tool sandbox path validation", () => {
     }
   });
 
+  it("rejects filePath file URL that escapes sandbox root", async () => {
+    const sandboxDir = await fs.mkdtemp(path.join(os.tmpdir(), "msg-sandbox-"));
+    try {
+      const tool = createMessageTool({
+        config: {} as never,
+        sandboxRoot: sandboxDir,
+      });
+
+      await expect(
+        tool.execute("1", {
+          action: "send",
+          target: "telegram:123",
+          filePath: "file:///etc/passwd",
+          message: "",
+        }),
+      ).rejects.toThrow(/sandbox/i);
+    } finally {
+      await fs.rm(sandboxDir, { recursive: true, force: true });
+    }
+  });
+
   it("rejects path param with traversal sequence", async () => {
     const sandboxDir = await fs.mkdtemp(path.join(os.tmpdir(), "msg-sandbox-"));
     try {
@@ -208,6 +229,59 @@ describe("message tool sandbox path validation", () => {
     }
   });
 
+  it("rejects media path that escapes sandbox root", async () => {
+    const sandboxDir = await fs.mkdtemp(path.join(os.tmpdir(), "msg-sandbox-"));
+    try {
+      const tool = createMessageTool({
+        config: {} as never,
+        sandboxRoot: sandboxDir,
+      });
+
+      await expect(
+        tool.execute("1", {
+          action: "send",
+          target: "telegram:123",
+          media: "/etc/passwd",
+          message: "",
+        }),
+      ).rejects.toThrow(/sandbox/i);
+    } finally {
+      await fs.rm(sandboxDir, { recursive: true, force: true });
+    }
+  });
+
+  it("allows remote media URLs inside sandbox", async () => {
+    mocks.runMessageAction.mockClear();
+    mocks.runMessageAction.mockResolvedValue({
+      kind: "send",
+      action: "send",
+      channel: "telegram",
+      to: "telegram:123",
+      handledBy: "plugin",
+      payload: {},
+      dryRun: true,
+    } satisfies MessageActionRunResult);
+
+    const sandboxDir = await fs.mkdtemp(path.join(os.tmpdir(), "msg-sandbox-"));
+    try {
+      const tool = createMessageTool({
+        config: {} as never,
+        sandboxRoot: sandboxDir,
+      });
+
+      await tool.execute("1", {
+        action: "send",
+        target: "telegram:123",
+        media: "https://example.com/file.png",
+        message: "",
+      });
+
+      expect(mocks.runMessageAction).toHaveBeenCalledTimes(1);
+    } finally {
+      await fs.rm(sandboxDir, { recursive: true, force: true });
+    }
+  });
+
   it("allows filePath inside sandbox root", async () => {
     mocks.runMessageAction.mockClear();
     mocks.runMessageAction.mockResolvedValue({
diff --git a/src/agents/tools/message-tool.ts b/src/agents/tools/message-tool.ts
index 359b075d2d..f294dc718d 100644
--- a/src/agents/tools/message-tool.ts
+++ b/src/agents/tools/message-tool.ts
@@ -1,4 +1,5 @@
 import { Type } from "@sinclair/typebox";
+import { fileURLToPath } from "node:url";
 import type { OpenClawConfig } from "../../config/config.js";
 import type { AnyAgentTool } from "./common.js";
 import { BLUEBUBBLES_GROUP_ACTIONS } from "../../channels/plugins/bluebubbles-actions.js";
@@ -24,6 +25,35 @@ import { channelTargetSchema, channelTargetsSchema, stringEnum } from "../schema
 import { jsonResult, readNumberParam, readStringParam } from "./common.js";
 
 const AllMessageActions = CHANNEL_MESSAGE_ACTION_NAMES;
+const REMOTE_SCHEME_PATTERN = /^[a-z][a-z0-9+.-]*:\/\//i;
+
+function normalizeSandboxPathInput(raw: string): string {
+  if (!raw.startsWith("file://")) {
+    return raw;
+  }
+  try {
+    return fileURLToPath(raw);
+  } catch {
+    throw new Error(`Invalid file:// URL: ${raw}`);
+  }
+}
+
+function shouldValidateMediaPath(value: string): boolean {
+  const trimmed = value.trim();
+  if (!trimmed) {
+    return false;
+  }
+  if (trimmed.startsWith("data:") || trimmed.startsWith("blob:")) {
+    return false;
+  }
+  if (trimmed.startsWith("file://")) {
+    return true;
+  }
+  if (REMOTE_SCHEME_PATTERN.test(trimmed)) {
+    return false;
+  }
+  return true;
+}
 function buildRoutingSchema() {
   return {
     channel: Type.Optional(Type.String()),
@@ -365,14 +395,22 @@ export function createMessageTool(options?: MessageToolOptions): AnyAgentTool {
       }) as ChannelMessageActionName;
 
       // Validate file paths against sandbox root to prevent host file access.
-      const sandboxRoot = options?.sandboxRoot;
+      const sandboxRoot = options?.sandboxRoot?.trim();
       if (sandboxRoot) {
+        const validatePath = async (raw: string) => {
+          const normalized = normalizeSandboxPathInput(raw);
+          await assertSandboxPath({ filePath: normalized, cwd: sandboxRoot, root: sandboxRoot });
+        };
         for (const key of ["filePath", "path"] as const) {
           const raw = readStringParam(params, key, { trim: false });
           if (raw) {
-            await assertSandboxPath({ filePath: raw, cwd: sandboxRoot, root: sandboxRoot });
+            await validatePath(raw);
           }
         }
+        const mediaRaw = readStringParam(params, "media", { trim: false });
+        if (mediaRaw && shouldValidateMediaPath(mediaRaw)) {
+          await validatePath(mediaRaw);
+        }
       }
 
       const accountId = readStringParam(params, "accountId") ?? agentAccountId;