@@ -138,6 +138,18 @@ function installFreeSocketDataGuard(socket) {
   }
 }
 
+// The data guard only runs when the event loop polls for I/O. Data that
+// reached the OS socket buffer after the last poll has not been seen by it
+// yet, so check for it directly before handing an idle socket to a request.
+function hasPendingRead(socket) {
+  // A socket that is still connecting has nothing to read yet, and a pending
+  // connect error must be reported to the request rather than swallowed here.
+  if (socket.connecting) return false;
+  const handle = socket._handle;
+  return typeof handle?.hasPendingRead === 'function' &&
+    handle.hasPendingRead() === true;
+}
+
 function removeFreeSocketDataGuard(socket) {
   if (socket[kFreeSocketDataGuard]) {
     socket.removeListener('connect', socket[kFreeSocketDataGuard]);
@@ -214,6 +226,12 @@ function Agent(options) {
 
     const requests = this.requests[name];
     if (requests?.length) {
+      if (hasPendingRead(socket)) {
+        // onClose() will create a new socket for the pending request.
+        debug('PENDING DATA on released socket - destroying');
+        socket.destroy();
+        return;
+      }
       const req = requests.shift();
       const reqAsyncRes = req[kRequestAsyncResource];
       if (reqAsyncRes) {
@@ -391,6 +409,13 @@ Agent.prototype.addRequest = function addRequest(req, options, port/* legacy */,
     socket = this.scheduling === 'fifo' ?
       freeSockets.shift() :
       freeSockets.pop();
+    while (socket && hasPendingRead(socket)) {
+      debug('PENDING DATA on FREE socket - destroying poisoned socket');
+      socket.destroy();
+      socket = this.scheduling === 'fifo' ?
+        freeSockets.shift() :
+        freeSockets.pop();
+    }
     if (!freeSockets.length)
       delete this.freeSockets[name];
   }
 
@@ -733,7 +733,7 @@ exports.TLSSocket = TLSSocket;
 const proxiedMethods = [
   'ref', 'unref', 'open', 'bind', 'listen', 'connect', 'bind6',
   'connect6', 'getsockname', 'getpeername', 'setNoDelay', 'setKeepAlive',
-  'setSimultaneousAccepts', 'setBlocking',
+  'setSimultaneousAccepts', 'setBlocking', 'hasPendingRead',
 
   // PipeWrap
   'setPendingInstances',
 
@@ -33,9 +33,9 @@
 #include "udp_wrap.h"
 #include "util-inl.h"
 
-#include <cstring>  // memcpy()
+#include <cerrno>   // errno
 #include <climits>  // INT_MAX
-
+#include <cstring>  // memcpy()
 
 namespace node {
 
@@ -130,6 +130,7 @@ void LibuvStreamWrap::RegisterExternalReferences(
   registry->Register(IsConstructCallCallback);
   registry->Register(GetWriteQueueSize);
   registry->Register(SetBlocking);
+  registry->Register(HasPendingRead);
   StreamBase::RegisterExternalReferences(registry);
 }
 
@@ -168,6 +169,7 @@ Local<FunctionTemplate> LibuvStreamWrap::GetConstructorTemplate(
         Local<FunctionTemplate>(),
         static_cast<PropertyAttribute>(ReadOnly | DontDelete));
     SetProtoMethod(isolate, tmpl, "setBlocking", SetBlocking);
+    SetProtoMethod(isolate, tmpl, "hasPendingRead", HasPendingRead);
     StreamBase::AddMethods(env, tmpl);
     env->set_libuv_stream_wrap_ctor_template(tmpl);
   }
@@ -335,6 +337,67 @@ void LibuvStreamWrap::SetBlocking(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(uv_stream_set_blocking(wrap->stream(), enable));
 }
 
+// Returns true if a read on the underlying socket would complete right now,
+// i.e. the OS has data, EOF, or a socket error queued that libuv has not
+// delivered yet because the event loop has not polled for I/O since it
+// arrived. Nothing is consumed. Returns false when there is nothing pending
+// or when the handle type does not support the check.
+void LibuvStreamWrap::HasPendingRead(const FunctionCallbackInfo<Value>& args) {
+  LibuvStreamWrap* wrap;
+  ASSIGN_OR_RETURN_UNWRAP(&wrap, args.This());
+  args.GetReturnValue().Set(false);
+
+  if (!wrap->IsAlive() || wrap->IsClosing()) return;
+
+#ifdef _WIN32
+  // Only TCP sockets can be probed with recv() on Windows.
+  if (!wrap->is_tcp()) return;
+#else
+  if (!wrap->is_tcp() && !wrap->is_named_pipe()) return;
+#endif
+
+  uv_os_fd_t fd;
+  if (uv_fileno(reinterpret_cast<uv_handle_t*>(wrap->stream()), &fd) != 0)
+    return;
+
+  char c;
+#ifdef _WIN32
+  // libuv puts TCP sockets in non-blocking mode and reads with zero-byte
+  // overlapped reads, so unread data stays in the kernel buffer.
+  int r = recv(reinterpret_cast<SOCKET>(fd), &c, 1, MSG_PEEK);
+  if (r == SOCKET_ERROR) {
+    switch (WSAGetLastError()) {
+      case WSAEWOULDBLOCK:
+      case WSAENOTCONN:
+      case WSAENOTSOCK:
+        return;
+    }
+  }
+#else
+  int flags = MSG_PEEK;
+#ifdef MSG_DONTWAIT
+  flags |= MSG_DONTWAIT;
+#endif
+  ssize_t r;
+  do {
+    r = recv(fd, &c, 1, flags);
+  } while (r == -1 && errno == EINTR);
+  if (r == -1) {
+    switch (errno) {
+      case EAGAIN:
+#if EWOULDBLOCK != EAGAIN
+      case EWOULDBLOCK:
+#endif
+      case ENOTCONN:
+      case ENOTSOCK:
+        return;
+    }
+  }
+#endif
+
+  args.GetReturnValue().Set(true);
+}
+
 typedef SimpleShutdownWrap<ReqWrap<uv_shutdown_t>> LibuvShutdownWrap;
 typedef SimpleWriteWrap<ReqWrap<uv_write_t>> LibuvWriteWrap;
 
 
@@ -108,6 +108,7 @@ class LibuvStreamWrap : public HandleWrap, public StreamBase {
   static void GetWriteQueueSize(
       const v8::FunctionCallbackInfo<v8::Value>& info);
   static void SetBlocking(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void HasPendingRead(const v8::FunctionCallbackInfo<v8::Value>& args);
 
   // Callbacks for libuv
   void OnUvAlloc(size_t suggested_size, uv_buf_t* buf);
 
@@ -0,0 +1,121 @@
+'use strict';
+
+// The free socket data guard in http.Agent only runs when the event loop
+// polls for I/O. If data reaches an idle socket's OS buffer and a request
+// takes that socket before the loop has polled, the guard never sees the data
+// and it would be parsed as the response to that request. The Agent must
+// check for pending data before handing a kept-alive socket to a request.
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+const poison =
+  'HTTP/1.1 200 OK\r\n' +
+  'X-Poisoned: true\r\n' +
+  'Connection: keep-alive\r\n' +
+  'Content-Length: 0\r\n' +
+  '\r\n';
+
+// Keep the event loop from polling until the bytes are in the client's
+// socket buffer, so libuv cannot deliver them to the data guard first.
+function waitForPendingRead(socket) {
+  const deadline = Date.now() + common.platformTimeout(5000);
+  while (!socket._handle.hasPendingRead()) {
+    assert.ok(Date.now() < deadline, 'timed out waiting for pending data');
+  }
+}
+
+function checkResponse(req, expectedBody, cb) {
+  req.on('response', common.mustCall((res) => {
+    let body = '';
+    res.setEncoding('utf8');
+    res.on('data', (chunk) => { body += chunk; });
+    res.on('end', common.mustCall(() => {
+      assert.strictEqual(res.headers['x-poisoned'], undefined);
+      assert.strictEqual(body, expectedBody);
+      cb?.(res);
+    }));
+  }));
+}
+
+// A socket taken from the free pool.
+{
+  let serverSocket;
+  const server = http.createServer(common.mustCall((req, res) => {
+    serverSocket ||= req.socket;
+    res.end(req.url);
+  }, 2));
+
+  server.listen(0, common.mustCall(() => {
+    const agent = new http.Agent({ keepAlive: true });
+    const options = { host: '127.0.0.1', port: server.address().port, agent };
+    const name = agent.getName(options);
+
+    const request1 = http.request({ ...options, path: '/request1' });
+    request1.end();
+    checkResponse(request1, '/request1');
+
+    request1.on('close', common.mustCall(() => {
+      process.nextTick(common.mustCall(() => {
+        assert.strictEqual(agent.freeSockets[name]?.length, 1);
+        const freeSocket = agent.freeSockets[name][0];
+
+        serverSocket.write(poison);
+        waitForPendingRead(freeSocket);
+
+        // Same tick: the loop has not polled since the data arrived.
+        const request2 = http.request({ ...options, path: '/request2' });
+        request2.end();
+
+        assert.strictEqual(freeSocket.destroyed, true);
+        assert.strictEqual(request2.reusedSocket, false);
+
+        checkResponse(request2, '/request2', common.mustCall(() => {
+          agent.destroy();
+          server.close();
+        }));
+      }));
+    }));
+  }));
+}
+
+// A released socket handed directly to a queued request.
+{
+  let serverSocket;
+  const server = http.createServer(common.mustCall((req, res) => {
+    serverSocket ||= req.socket;
+    res.end(req.url);
+  }, 2));
+
+  server.listen(0, common.mustCall(() => {
+    const agent = new http.Agent({ keepAlive: true, maxSockets: 1 });
+    const options = { host: '127.0.0.1', port: server.address().port, agent };
+    const name = agent.getName(options);
+
+    const request1 = http.request({ ...options, path: '/request1' });
+    request1.end();
+    const request2 = http.request({ ...options, path: '/request2' });
+    request2.end();
+    assert.strictEqual(agent.requests[name]?.length, 1);
+
+    let socket1;
+    request1.on('socket', common.mustCall((socket) => {
+      socket1 = socket;
+    }));
+
+    // The socket is released to the queued request on the next tick after
+    // 'end', so the loop does not poll in between.
+    checkResponse(request1, '/request1', common.mustCall(() => {
+      serverSocket.write(poison);
+      waitForPendingRead(socket1);
+    }));
+
+    checkResponse(request2, '/request2', common.mustCall(() => {
+      assert.strictEqual(socket1.destroyed, true);
+      assert.strictEqual(request2.reusedSocket, false);
+      agent.destroy();
+      server.close();
+    }));
+  }));
+}