diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index c2c07f0f..49397a8c 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -23,3 +23,7 @@
 **Vulnerability:** The `CorsRequestHandler.java` implementation blindly read the `Origin` header from incoming HTTP requests and reflected its exact value back in the `Access-Control-Allow-Origin` response header.
 **Learning:** Blindly mirroring the request's origin bypasses the intended security of CORS restrictions and can lead to arbitrary cross-origin data exposure, effectively negating the same-origin policy enforcement by browsers. Moreover, doing so without `Vary: Origin` could lead to cache poisoning in intermediate CDNs.
 **Prevention:** Hardcode public API endpoint CORS rules to return the explicitly permissive `*` (wildcard) instead of reflecting the user's string input.
+## 2026-09-29 - Prevent Path Traversal in LeaseFileLockingService and LeaseFileMutex
+**Vulnerability:** A Path Traversal vulnerability existed in `LeaseFileLockingService` and `LeaseFileMutex` where the `UploadId` was blindly resolved against the base storage directory to construct `.lock`, `.stop`, and `.mutex` paths.
+**Learning:** Similar to the previous issue in `AbstractDiskBasedService`, any paths constructed from `UploadId` input must be properly normalized and constrained to the base storage directory, as unvalidated `UploadId`s could lead to out-of-bounds file access or creation.
+**Prevention:** Always validate that constructed file paths derived from user input or external identifiers remain within their intended boundary directory by using `path.normalize().toAbsolutePath().startsWith(storagePath.normalize().toAbsolutePath())`. Ensure this check is consistently applied across all file-based services.
diff --git a/src/main/java/me/desair/tus/server/upload/disk/LeaseFileLockingService.java b/src/main/java/me/desair/tus/server/upload/disk/LeaseFileLockingService.java
index 90b17823..f144f25d 100644
--- a/src/main/java/me/desair/tus/server/upload/disk/LeaseFileLockingService.java
+++ b/src/main/java/me/desair/tus/server/upload/disk/LeaseFileLockingService.java
@@ -374,18 +374,28 @@ boolean atomicEvictExpiredLock(Path lockDirPath) {
     }
   }
 
-  Path getLockDirPath(UploadId id) {
+  Path getLockDirPath(final UploadId id) {
     if (id == null) {
       return null;
     }
-    return storagePath.resolve(id.toString() + ".lock");
+    Path path = storagePath.resolve(id.toString() + ".lock");
+    if (!path.normalize().toAbsolutePath().startsWith(storagePath.normalize().toAbsolutePath())) {
+      throw new IllegalArgumentException(
+          "Upload ID is not valid and would result in a path traversal");
+    }
+    return path;
   }
 
-  Path getStopFilePath(UploadId id) {
+  Path getStopFilePath(final UploadId id) {
     if (id == null) {
       return null;
     }
-    return storagePath.resolve(id.toString() + ".stop");
+    Path path = storagePath.resolve(id.toString() + ".stop");
+    if (!path.normalize().toAbsolutePath().startsWith(storagePath.normalize().toAbsolutePath())) {
+      throw new IllegalArgumentException(
+          "Upload ID is not valid and would result in a path traversal");
+    }
+    return path;
   }
 
   private synchronized void initStoragePath() {
diff --git a/src/main/java/me/desair/tus/server/upload/disk/LeaseFileMutex.java b/src/main/java/me/desair/tus/server/upload/disk/LeaseFileMutex.java
index 1d7909e4..e6618fbd 100644
--- a/src/main/java/me/desair/tus/server/upload/disk/LeaseFileMutex.java
+++ b/src/main/java/me/desair/tus/server/upload/disk/LeaseFileMutex.java
@@ -45,11 +45,17 @@ public LeaseFileMutex(Path lockDirPath) {
    * @param storagePath Path to the base locks storage directory
    * @param uploadId The upload identifier
    */
-  public LeaseFileMutex(Path storagePath, UploadId uploadId) {
-    this.mutexDir =
-        (storagePath != null && uploadId != null)
-            ? storagePath.resolve(uploadId.toString() + ".mutex")
-            : null;
+  public LeaseFileMutex(final Path storagePath, final UploadId uploadId) {
+    if (storagePath != null && uploadId != null) {
+      Path path = storagePath.resolve(uploadId.toString() + ".mutex");
+      if (!path.normalize().toAbsolutePath().startsWith(storagePath.normalize().toAbsolutePath())) {
+        throw new IllegalArgumentException(
+            "Upload ID is not valid and would result in a path traversal");
+      }
+      this.mutexDir = path;
+    } else {
+      this.mutexDir = null;
+    }
     this.acquired = tryAcquire();
   }