diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index e0fa46b..d491623 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,8 @@
 **Vulnerability:** API endpoints in `backend/src/server.ts` taking user input (`projectId`, `jobId`) were directly joined with paths using `join` in `backend/src/store/localStore.ts` without proper sanitization. This allowed attackers to escape the project directory context and overwrite or read arbitrary files by sending payload containing `../` sequences.
 **Learning:** Even internal backend services handling project resources must securely sanitize all parameter values used for file operations to prevent path traversal outside expected boundaries.
 **Prevention:** Always use safe path sanitization utilities, like the implemented `safeJoin` and `toSafeRelativePath` in `backend/src/utils/path.ts`, to securely construct file paths and ensure the final path remains within the intended boundaries.
+
+## 2024-05-24 - [Command Injection via Option Injection]
+**Vulnerability:** The Rust compile worker directly passed `req.main_file` to `latexmk` without validation. Attackers could supply filenames starting with a hyphen (e.g., `-shell-escape`) to inject arguments via array-based argument passing (`spawn`).
+**Learning:** Even when using safer array-based argument passing instead of shell interpolation, user input intended as positional arguments (like filenames) can be misinterpreted as options if they start with hyphens.
+**Prevention:** Explicitly validate and reject user-provided filenames or paths that start with a hyphen (`-`) if they are to be passed as positional arguments to command line tools.
diff --git a/backend/src/services/compileQueue.ts b/backend/src/services/compileQueue.ts
index ed1a3e6..15e9e31 100644
--- a/backend/src/services/compileQueue.ts
+++ b/backend/src/services/compileQueue.ts
@@ -101,6 +101,13 @@ export class CompileQueueService {
     const settings = await this.store.getSettings();
     const projectId = request.projectId.trim();
     const mainFile = request.mainFile?.trim() || "main.tex";
+
+    // Prevent option injection (Command Injection) via filenames starting with "-"
+    // e.g. -shell-escape which would be evaluated as a flag by latexmk
+    if (mainFile.startsWith("-")) {
+      throw new HttpError(400, "mainFile cannot start with a hyphen.");
+    }
+
     const timeoutMs = request.timeoutMs ?? settings.compileTimeoutMs;
     const jobId = createId("job");