diff --git a/include/html_util.h b/include/html_util.h
index 5ed1db4..02c96b4 100644
--- a/include/html_util.h
+++ b/include/html_util.h
@@ -4,3 +4,4 @@
 
 String html_escape(const String &input);
 String url_encode_component(const String &input);
+bool sanitize_device_id(const String &input, String &out_device_id);
diff --git a/src/html_util.cpp b/src/html_util.cpp
index dff470f..51b79d4 100644
--- a/src/html_util.cpp
+++ b/src/html_util.cpp
@@ -47,3 +47,52 @@ String url_encode_component(const String &input) {
   }
   return out;
 }
+
+static bool is_hex_char(char c) {
+  return (c >= '0' && c <= '9') ||
+      (c >= 'a' && c <= 'f') ||
+      (c >= 'A' && c <= 'F');
+}
+
+static String to_upper_hex4(const String &input) {
+  String out = input;
+  out.toUpperCase();
+  return out;
+}
+
+bool sanitize_device_id(const String &input, String &out_device_id) {
+  String trimmed = input;
+  trimmed.trim();
+  if (trimmed.length() == 0) {
+    return false;
+  }
+  if (trimmed.indexOf('/') >= 0 || trimmed.indexOf('\\') >= 0 || trimmed.indexOf("..") >= 0) {
+    return false;
+  }
+  if (trimmed.indexOf('%') >= 0) {
+    return false;
+  }
+
+  if (trimmed.length() == 4) {
+    for (size_t i = 0; i < 4; ++i) {
+      if (!is_hex_char(trimmed[i])) {
+        return false;
+      }
+    }
+    out_device_id = String("dd3-") + to_upper_hex4(trimmed);
+    return true;
+  }
+
+  if (trimmed.length() == 8 && trimmed.startsWith("dd3-")) {
+    String hex = trimmed.substring(4);
+    for (size_t i = 0; i < 4; ++i) {
+      if (!is_hex_char(hex[i])) {
+        return false;
+      }
+    }
+    out_device_id = String("dd3-") + to_upper_hex4(hex);
+    return true;
+  }
+
+  return false;
+}
diff --git a/src/web_server.cpp b/src/web_server.cpp
index c5d2bc7..e457a4e 100644
--- a/src/web_server.cpp
+++ b/src/web_server.cpp
@@ -140,6 +140,42 @@ static bool checkbox_checked(const char *name) {
   return val == "on" || val == "true" || val == "1";
 }
 
+static bool sanitize_history_device_id(const String &input, String &out_device_id) {
+  if (sanitize_device_id(input, out_device_id)) {
+    return true;
+  }
+  if (g_statuses) {
+    for (uint8_t i = 0; i < g_status_count; ++i) {
+      String known = g_statuses[i].last_data.device_id;
+      if (input.equalsIgnoreCase(known) && sanitize_device_id(known, out_device_id)) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+static String sanitize_download_filename(const String &input, bool &clean) {
+  String out;
+  out.reserve(input.length());
+  clean = true;
+  for (size_t i = 0; i < input.length(); ++i) {
+    unsigned char c = static_cast<unsigned char>(input[i]);
+    if (c < 32 || c == 127 || c == '"' || c == '\\' || c == '/') {
+      out += '_';
+      clean = false;
+      continue;
+    }
+    out += static_cast<char>(c);
+  }
+  out.trim();
+  if (out.length() == 0) {
+    out = "download.bin";
+    clean = false;
+  }
+  return out;
+}
+
 static void history_reset() {
   if (g_history.file) {
     g_history.file.close();
@@ -597,7 +633,12 @@ static void handle_history_start() {
     server.send(200, "application/json", "{\"ok\":false,\"error\":\"time_not_synced\"}");
     return;
   }
-  String device_id = server.arg("device_id");
+  String device_id_arg = server.arg("device_id");
+  String device_id;
+  if (!sanitize_history_device_id(device_id_arg, device_id)) {
+    server.send(200, "application/json", "{\"ok\":false,\"error\":\"bad_device_id\"}");
+    return;
+  }
   uint16_t days = static_cast<uint16_t>(server.arg("days").toInt());
   uint16_t res_min = static_cast<uint16_t>(server.arg("res").toInt());
   String mode_str = server.arg("mode");
@@ -652,7 +693,12 @@ static void handle_history_data() {
   if (!ensure_auth()) {
     return;
   }
-  String device_id = server.arg("device_id");
+  String device_id_arg = server.arg("device_id");
+  String device_id;
+  if (!sanitize_history_device_id(device_id_arg, device_id)) {
+    server.send(200, "application/json", "{\"ready\":false,\"error\":\"bad_device_id\"}");
+    return;
+  }
   if (!g_history.bins || device_id.length() == 0 || device_id != g_history.device_id) {
     server.send(200, "application/json", "{\"ready\":false,\"error\":\"no_job\"}");
     return;
@@ -716,7 +762,11 @@ static void handle_sd_download() {
   }
   size_t size = f.size();
   String filename = path.substring(path.lastIndexOf('/') + 1);
-  server.sendHeader("Content-Disposition", "attachment; filename=\"" + filename + "\"");
+  bool name_clean = true;
+  (void)name_clean;
+  String safe_name = sanitize_download_filename(filename, name_clean);
+  String cd = "attachment; filename=\"" + safe_name + "\"; filename*=UTF-8''" + url_encode_component(safe_name);
+  server.sendHeader("Content-Disposition", cd);
   server.setContentLength(size);
   const char *content_type = "application/octet-stream";
   if (filename.endsWith(".csv")) {
diff --git a/test/test_html_escape/test_html_escape.cpp b/test/test_html_escape/test_html_escape.cpp
index 6ffbf8f..2f782cc 100644
--- a/test/test_html_escape/test_html_escape.cpp
+++ b/test/test_html_escape/test_html_escape.cpp
@@ -12,9 +12,25 @@ static void test_html_escape_basic() {
   TEST_ASSERT_EQUAL_STRING("&amp;&lt;&gt;&quot;&#39;", html_escape("&<>\"'").c_str());
 }
 
+static void test_sanitize_device_id() {
+  String out;
+  TEST_ASSERT_TRUE(sanitize_device_id("F19C", out));
+  TEST_ASSERT_EQUAL_STRING("dd3-F19C", out.c_str());
+  TEST_ASSERT_TRUE(sanitize_device_id("dd3-f19c", out));
+  TEST_ASSERT_EQUAL_STRING("dd3-F19C", out.c_str());
+  TEST_ASSERT_FALSE(sanitize_device_id("F19G", out));
+  TEST_ASSERT_FALSE(sanitize_device_id("dd3-12", out));
+  TEST_ASSERT_FALSE(sanitize_device_id("dd3-12345", out));
+  TEST_ASSERT_FALSE(sanitize_device_id("../F19C", out));
+  TEST_ASSERT_FALSE(sanitize_device_id("dd3-%2f", out));
+  TEST_ASSERT_FALSE(sanitize_device_id("dd3-12/3", out));
+  TEST_ASSERT_FALSE(sanitize_device_id("dd3-12\\3", out));
+}
+
 void setup() {
   UNITY_BEGIN();
   RUN_TEST(test_html_escape_basic);
+  RUN_TEST(test_sanitize_device_id);
   UNITY_END();
 }