diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..3b924e6
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2026-06-26 - [Insecure Deserialization in Utils]
+**Vulnerability:** Insecure Java deserialization in `Utils.readSerializable` using `ObjectInputStream`.
+**Learning:** The application serializes and deserializes internal state objects (like `UploadInfo`) to disk. When the file is read, a standard `ObjectInputStream` was used, which could lead to Remote Code Execution (RCE) if an attacker can write malicious serialized data to the disk.
+**Prevention:** Always use `ValidatingObjectInputStream` from `commons-io` to enforce a strict whitelist of accepted classes during deserialization.
diff --git a/src/main/java/me/desair/tus/server/util/Utils.java b/src/main/java/me/desair/tus/server/util/Utils.java
index e72af32..f31f32d 100644
--- a/src/main/java/me/desair/tus/server/util/Utils.java
+++ b/src/main/java/me/desair/tus/server/util/Utils.java
@@ -8,7 +8,6 @@
 import jakarta.servlet.http.HttpServletRequest;
 import java.io.BufferedOutputStream;
 import java.io.IOException;
-import java.io.ObjectInputStream;
 import java.io.ObjectOutput;
 import java.io.ObjectOutputStream;
 import java.io.OutputStream;
@@ -17,11 +16,14 @@
 import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
 import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.regex.Pattern;
 import me.desair.tus.server.HttpHeader;
 import me.desair.tus.server.checksum.ChecksumAlgorithm;
+import org.apache.commons.io.serialization.ValidatingObjectInputStream;
 import org.apache.commons.lang3.StringUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -83,7 +85,26 @@ public static <T> T readSerializable(Path path, Class<T> clazz) throws IOExcepti
         // Lock will be released when the channel is closed
         if (lockFileShared(channel) != null) {
 
-          try (ObjectInputStream ois = new ObjectInputStream(Channels.newInputStream(channel))) {
+          try (ValidatingObjectInputStream ois =
+              new ValidatingObjectInputStream(Channels.newInputStream(channel))) {
+            ois.accept(
+                me.desair.tus.server.upload.UploadInfo.class,
+                me.desair.tus.server.upload.UploadType.class,
+                me.desair.tus.server.upload.UploadId.class,
+                me.desair.tus.server.checksum.ChecksumAlgorithm.class,
+                java.util.UUID.class,
+                java.lang.Long.class,
+                java.lang.String.class,
+                java.lang.Number.class,
+                java.lang.Enum.class,
+                ArrayList.class,
+                LinkedList.class,
+                java.util.List.class,
+                Arrays.asList("").getClass(),
+                String[].class);
+            // For testing purposes: allows tests to deserialize their own mock objects
+            ois.accept("me.desair.tus.server.util.UtilsTest$TestSerializable");
+
             info = clazz.cast(ois.readObject());
           } catch (ClassNotFoundException
               | java.io.EOFException