diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4b88c700ae12..f82cf606f75e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,7 @@ Docs: https://docs.openclaw.ai
 - Browser tool: treat malformed node proxy `payloadJSON` responses as browser proxy failures instead of leaking raw JSON parser errors.
 - Gateway HTTP: match models, session kill, and session history route paths without trusting malformed Host headers, avoiding pre-auth 500s on those endpoints.
 - Google Meet/Codex: report malformed node proxy `payloadJSON` responses with plugin-owned errors instead of leaking raw JSON parser failures.
+- Debug proxy: reject malformed relative-form proxy targets with a controlled 400 response instead of letting URL parsing escape the request handler.
 - Models config/auth: stop inferring provider env-var markers from broad `^[A-Z_][A-Z0-9_]*$` strings, and resolve config-backed provider `apiKey` values only through structured env SecretRefs (`secrets.providers[id]` / `secrets.defaults`), so unrelated env vars cannot accidentally become provider credentials. Thanks @sallyom.
 - Media fetch: skip allocating and buffering the response body for bodyless media responses (HEAD probes and 204-style empty bodies), avoiding wasted heap on streams that carry no payload. Thanks @shakkernerd.
 - CLI/onboarding: forward provider-specific auth flags (e.g. `--openai-api-key`) through the onboarding wizard so they reach provider auth methods via `ctx.opts`, letting `--openai-api-key "$OPENAI_API_KEY"` skip the redundant "use existing env var?" prompt in non-interactive harnesses. (#81669) Thanks @sjf.
diff --git a/src/proxy-capture/proxy-server.managed-proxy.test.ts b/src/proxy-capture/proxy-server.managed-proxy.test.ts
index d25b71091697..7dabfb79690e 100644
--- a/src/proxy-capture/proxy-server.managed-proxy.test.ts
+++ b/src/proxy-capture/proxy-server.managed-proxy.test.ts
@@ -71,6 +71,24 @@ async function requestThroughProxy(proxyUrl: string, targetUrl: string): Promise
   return data;
 }
 
+async function requestRawThroughProxy(proxyUrl: string, request: string): Promise<string> {
+  const proxy = new URL(proxyUrl);
+  const socket = new Socket();
+  let data = "";
+  socket.setEncoding("utf8");
+  socket.on("data", (chunk) => {
+    data += chunk;
+  });
+  await new Promise<void>((resolve, reject) => {
+    socket.once("error", reject);
+    socket.connect(Number(proxy.port), proxy.hostname, resolve);
+  });
+  socket.write(request);
+  await new Promise<void>((resolve) => socket.once("end", resolve));
+  socket.destroy();
+  return data;
+}
+
 async function startCanaryOrigin(): Promise<{
   requestCount: () => number;
   stop: () => Promise<void>;
@@ -188,4 +206,20 @@ describe("debug proxy managed-proxy direct upstream policy", () => {
       await origin.stop();
     }
   });
+
+  it("rejects malformed relative-form HTTP proxy targets before upstream handling", async () => {
+    const server = await startDebugProxyServer({ settings: await makeSettings() });
+    try {
+      const response = await requestRawThroughProxy(
+        server.proxyUrl,
+        "GET /capture HTTP/1.1\r\nHost: [\r\nConnection: close\r\n\r\n",
+      );
+
+      expect(response).toContain("400 Bad Request");
+      expect(response).toContain("Connection: close");
+      expect(response).toContain("Invalid proxy target URL");
+    } finally {
+      await server.stop();
+    }
+  });
 });
diff --git a/src/proxy-capture/proxy-server.ts b/src/proxy-capture/proxy-server.ts
index 3ea799b47104..c702f6b77c08 100644
--- a/src/proxy-capture/proxy-server.ts
+++ b/src/proxy-capture/proxy-server.ts
@@ -98,7 +98,34 @@ export async function startDebugProxyServer(params: {
 
   const server = createServer(async (req: IncomingMessage, res: ServerResponse) => {
     const flowId = randomUUID();
-    const target = normalizeTargetUrl(req);
+    let target: URL;
+    try {
+      target = normalizeTargetUrl(req);
+    } catch (error) {
+      const message = "Invalid proxy target URL";
+      store.recordEvent({
+        sessionId: params.settings.sessionId,
+        ts: Date.now(),
+        sourceScope: "openclaw",
+        sourceProcess: params.settings.sourceProcess,
+        protocol: "http",
+        direction: "local",
+        kind: "error",
+        flowId,
+        method: req.method,
+        host: req.headers.host,
+        path: req.url ?? "",
+        errorText: error instanceof Error ? error.message : String(error),
+      });
+      const responseBody = `${message}\n`;
+      res.writeHead(400, {
+        Connection: "close",
+        "Content-Type": "text/plain; charset=utf-8",
+        "Content-Length": Buffer.byteLength(responseBody),
+      });
+      res.end(responseBody);
+      return;
+    }
     try {
       assertDebugProxyDirectUpstreamAllowed();
     } catch (error) {