🛡️ Sentinel: [CRITICAL] Fixed insecure file permission modification

.jules/sentinel.md

@@ -48,3 +48,7 @@
 **Learning:** High-level Swift file writing APIs do not natively protect against malicious symlinks in untrusted directories, potentially allowing unintended files to be overwritten or appended to.
 **Prevention:** Always use POSIX `open(2)` with `O_CREAT | O_WRONLY | O_APPEND | O_NOFOLLOW | O_CLOEXEC` to securely refuse symlink traversal, then wrap the resulting file descriptor in a `FileHandle`. Ensure directories are also securely created using `.posixPermissions`.
 
+## 2026-05-02 - Insecure File Permissions Update
+**Vulnerability:** Found insecure permission modification that could be redirected.
+**Learning:** Permission modification APIs that use string paths can be redirected via symlinks.
+**Prevention:** Always use POSIX open() with O_NOFOLLOW and apply permissions with fchmod().

Sources/Cacheout/Headless/DaemonMode.swift

@@ -295,10 +295,22 @@ public actor DaemonMode: StatusSocket.DataSource {
                 withIntermediateDirectories: true,
                 attributes: [.posixPermissions: 0o700]
             )
-            try FileManager.default.setAttributes(
-                [.posixPermissions: 0o700],
-                ofItemAtPath: config.stateDir.path
-            )
+            // SECURITY: Use open with O_NOFOLLOW and fchmod to prevent TOCTOU symlink attacks
+            // when setting permissions on the state directory.
+            struct SecureOperationError: Error {}
+            let dirFd = config.stateDir.withUnsafeFileSystemRepresentation { pathPtr -> Int32 in
+                guard let pathPtr = pathPtr else { return -1 }
+                return open(pathPtr, O_RDONLY | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC)
+            }
+            if dirFd >= 0 {
+                if fchmod(dirFd, 0o700) != 0 {
+                    close(dirFd)
+                    throw SecureOperationError()
+                }
+                close(dirFd)
+            } else {
+                throw SecureOperationError()
+            }
         } catch {
             logger.error("Failed to create/secure state directory: \(error.localizedDescription, privacy: .public)")
             Foundation.exit(1)