diff --git a/Emulator/src/main/java/com/eu/habbo/messages/rcon/UpdateUser.java b/Emulator/src/main/java/com/eu/habbo/messages/rcon/UpdateUser.java
index 7357a760..14800d18 100644
--- a/Emulator/src/main/java/com/eu/habbo/messages/rcon/UpdateUser.java
+++ b/Emulator/src/main/java/com/eu/habbo/messages/rcon/UpdateUser.java
@@ -12,9 +12,13 @@ import org.slf4j.LoggerFactory;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.SQLException;
+import java.util.regex.Pattern;
 
 public class UpdateUser extends RCONMessage<UpdateUser.JSON> {
     private static final Logger LOGGER = LoggerFactory.getLogger(UpdateUser.class);
+    static final int DEFAULT_MAX_ACHIEVEMENT_SCORE_DELTA = 10_000;
+    static final int MAX_LOOK_LENGTH = 256;
+    private static final Pattern LOOK_PATTERN = Pattern.compile("^[A-Za-z0-9.-]{1,256}$");
 
     public UpdateUser() {
         super(UpdateUser.JSON.class);
@@ -23,6 +27,19 @@ public class UpdateUser extends RCONMessage<UpdateUser.JSON> {
     @Override
     public void handle(Gson gson, JSON json) {
         if (json.user_id > 0) {
+            int maxAchievementScoreDelta = parseMaxAchievementScoreDelta(Emulator.getConfig().getValue("rcon.updateuser.max_achievement_score_delta", String.valueOf(DEFAULT_MAX_ACHIEVEMENT_SCORE_DELTA)));
+            if (!isValidAchievementScoreDelta(json.achievement_score, maxAchievementScoreDelta)) {
+                this.status = RCONMessage.STATUS_ERROR;
+                this.message = "invalid achievement score";
+                return;
+            }
+
+            if (!isValidLook(json.look)) {
+                this.status = RCONMessage.STATUS_ERROR;
+                this.message = "invalid look";
+                return;
+            }
+
             Habbo habbo = Emulator.getGameEnvironment().getHabboManager().getHabbo(json.user_id);
 
             if (habbo != null) {
@@ -97,23 +114,56 @@ public class UpdateUser extends RCONMessage<UpdateUser.JSON> {
                             index++;
                         }
                         statement.setInt(index, json.user_id);
-                        statement.execute();
+                        if (statement.executeUpdate() == 0) {
+                            this.status = RCONMessage.HABBO_NOT_FOUND;
+                            this.message = "user not found";
+                            return;
+                        }
                     }
 
                     if (!json.look.isEmpty()) {
                         try (PreparedStatement statement = connection.prepareStatement("UPDATE users SET look = ? WHERE id = ? LIMIT 1")) {
                             statement.setString(1, json.look);
                             statement.setInt(2, json.user_id);
-                            statement.execute();
+                            if (statement.executeUpdate() == 0) {
+                                this.status = RCONMessage.HABBO_NOT_FOUND;
+                                this.message = "user not found";
+                                return;
+                            }
                         }
                     }
                 } catch (SQLException e) {
                     LOGGER.error("Caught SQL exception", e);
+                    this.status = RCONMessage.SYSTEM_ERROR;
+                    this.message = "failed to update user";
                 }
             }
+        } else {
+            this.status = RCONMessage.STATUS_ERROR;
+            this.message = "invalid user";
         }
     }
 
+    static boolean isValidAchievementScoreDelta(int achievementScoreDelta, int maxAchievementScoreDelta) {
+        return achievementScoreDelta >= 0 && achievementScoreDelta <= maxAchievementScoreDelta;
+    }
+
+    static int parseMaxAchievementScoreDelta(String configured) {
+        try {
+            int parsed = Integer.parseInt(configured);
+            if (parsed >= 0) {
+                return parsed;
+            }
+        } catch (NumberFormatException ignored) {
+        }
+
+        return DEFAULT_MAX_ACHIEVEMENT_SCORE_DELTA;
+    }
+
+    static boolean isValidLook(String look) {
+        return look == null || look.isEmpty() || (look.length() <= MAX_LOOK_LENGTH && LOOK_PATTERN.matcher(look).matches());
+    }
+
     static class JSON {
 
         public int user_id;
@@ -142,4 +192,4 @@ public class UpdateUser extends RCONMessage<UpdateUser.JSON> {
         public boolean strip_unredeemed_clothing = false;
         //More could be added in the future.
     }
-}
\ No newline at end of file
+}
diff --git a/Emulator/src/test/java/com/eu/habbo/messages/rcon/UpdateUserGuardTest.java b/Emulator/src/test/java/com/eu/habbo/messages/rcon/UpdateUserGuardTest.java
new file mode 100644
index 00000000..0ca4dc2a
--- /dev/null
+++ b/Emulator/src/test/java/com/eu/habbo/messages/rcon/UpdateUserGuardTest.java
@@ -0,0 +1,50 @@
+package com.eu.habbo.messages.rcon;
+
+import org.junit.jupiter.api.Test;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class UpdateUserGuardTest {
+    @Test
+    void validatesAchievementScoreDelta() {
+        assertTrue(UpdateUser.isValidAchievementScoreDelta(0, 100));
+        assertTrue(UpdateUser.isValidAchievementScoreDelta(100, 100));
+        assertFalse(UpdateUser.isValidAchievementScoreDelta(-1, 100));
+        assertFalse(UpdateUser.isValidAchievementScoreDelta(101, 100));
+    }
+
+    @Test
+    void parsesInvalidAchievementScoreCeilingsAsDefault() {
+        assertEquals(UpdateUser.DEFAULT_MAX_ACHIEVEMENT_SCORE_DELTA, UpdateUser.parseMaxAchievementScoreDelta(null));
+        assertEquals(UpdateUser.DEFAULT_MAX_ACHIEVEMENT_SCORE_DELTA, UpdateUser.parseMaxAchievementScoreDelta("-1"));
+        assertEquals(0, UpdateUser.parseMaxAchievementScoreDelta("0"));
+        assertEquals(50, UpdateUser.parseMaxAchievementScoreDelta("50"));
+    }
+
+    @Test
+    void validatesLookShapeAndLength() {
+        assertTrue(UpdateUser.isValidLook(null));
+        assertTrue(UpdateUser.isValidLook(""));
+        assertTrue(UpdateUser.isValidLook("hr-115-42.hd-195-19.ch-3030-82"));
+        assertFalse(UpdateUser.isValidLook("hd-1\nch-1"));
+        assertFalse(UpdateUser.isValidLook("hd_1"));
+        assertFalse(UpdateUser.isValidLook("a".repeat(UpdateUser.MAX_LOOK_LENGTH + 1)));
+    }
+
+    @Test
+    void offlineUpdatesReportMissingUsersAndUseAffectedRows() throws Exception {
+        String source = Files.readString(Path.of("src/main/java/com/eu/habbo/messages/rcon/UpdateUser.java"));
+
+        assertTrue(source.contains("executeUpdate() == 0"),
+                "Offline UpdateUser mutations must inspect affected row counts");
+        assertTrue(source.contains("HABBO_NOT_FOUND"),
+                "Offline UpdateUser mutations must report missing users");
+        assertTrue(source.contains("rcon.updateuser.max_achievement_score_delta"),
+                "Achievement score deltas must have a configurable RCON ceiling");
+    }
+}