🛡️ Sentinel: [CRITICAL] Fix Path Traversal in FileSystemContext::new

.jules/sentinel.md

@@ -0,0 +1,4 @@
+## 2026-05-04 - Path Traversal bypass via uncanonicalized base path in FileSystemContext::new
+**Vulnerability:** The `FileSystemContext::new` method previously accepted a `base_path` and stored it as-is without canonicalization. Later on, `FileSystemContext::secure_path` validated requested paths by joining them with the `base_path` and checking that it `starts_with` the `base_path`, then canonicalizing the base path _just_ to check symlink escapes. If the `base_path` wasn't fully resolved initially, clever manipulation of paths with `..` relative to uncanonicalized base paths combined with symlinks could slip past the starts_with lexical check before the physical check triggered correctly.
+**Learning:** An uncanonicalized base directory breaks lexical boundary checks. When checking bounds (`starts_with`) on a potentially dangerous path relative to a base path, the base path itself must be canonicalized _before_ the context is ever used to ensure uniform comparison.
+**Prevention:** Canonicalize the absolute base directory upfront during object construction and fail immediately if it cannot be resolved.

crates/services/src/lib.rs

@@ -142,10 +142,15 @@ pub struct FileSystemContext {
 }
 
 impl FileSystemContext {
-    pub fn new<P: AsRef<Path>>(base_path: P) -> Self {
-        Self {
-            base_path: base_path.as_ref().to_path_buf(),
-        }
+    pub fn new<P: AsRef<Path>>(base_path: P) -> ServiceResult<Self> {
+        let canonical_base = base_path
+            .as_ref()
+            .canonicalize()
+            .map_err(|e| ServiceError::execution_dynamic(format!("Invalid base path: {}", e)))?;
+
+        Ok(Self {
+            base_path: canonical_base,
+        })
     }
 
     /// Lexically validate path to prevent traversal attacks and symlink escapes
@@ -310,7 +315,7 @@ mod tests {
     #[test]
     fn test_file_system_context_security() {
         let temp = std::env::temp_dir();
-        let ctx = FileSystemContext::new(&temp);
+        let ctx = FileSystemContext::new(&temp).unwrap();
 
         // Valid paths
         assert!(ctx.secure_path("test.txt").is_ok());

crates/thread/tests/integration.rs

@@ -18,5 +18,5 @@ fn test_service_reexports_work() {
     use thread::services::FileSystemContext;
 
     // Just check if we can use the types
-    let _ctx = FileSystemContext::new(".");
+    let _ctx = FileSystemContext::new(".").unwrap();
 }