fix(filesystem): preserve UNC path prefix during normalization

src/filesystem/__tests__/path-validation.test.ts

@@ -997,4 +997,24 @@ describe('Path Validation', () => {
       expect(forbiddenContent).toBe('ORIGINAL CONTENT'); // Unchanged
     });
   });
+
+  describe('UNC paths (Windows network shares)', () => {
+    // UNC path tests use string-only checks (no filesystem access needed)
+    it('should accept files within a UNC allowed directory', () => {
+      const allowed = ['\\\\server\\share'];
+      expect(isPathWithinAllowedDirectories('\\\\server\\share\\file.txt', allowed)).toBe(true);
+      expect(isPathWithinAllowedDirectories('\\\\server\\share\\sub\\deep.txt', allowed)).toBe(true);
+    });
+
+    it('should reject files outside a UNC allowed directory', () => {
+      const allowed = ['\\\\server\\share'];
+      expect(isPathWithinAllowedDirectories('\\\\server\\other\\file.txt', allowed)).toBe(false);
+      expect(isPathWithinAllowedDirectories('\\\\other-server\\share\\file.txt', allowed)).toBe(false);
+    });
+
+    it('should accept the UNC directory itself', () => {
+      const allowed = ['\\\\server\\share'];
+      expect(isPathWithinAllowedDirectories('\\\\server\\share', allowed)).toBe(true);
+    });
+  });
 });

src/filesystem/path-validation.ts

@@ -1,5 +1,21 @@
 import path from 'path';
 
+/**
+ * Normalize a path, preserving UNC prefix on Windows.
+ * path.normalize can strip one leading backslash from UNC paths
+ * (e.g. \\\\server\\share → \\server\\share), and path.resolve then
+ * misinterprets the single-backslash path as drive-relative.
+ */
+function safeNormalize(p: string): string {
+  const isUNC = p.startsWith('\\\\');
+  let normalized = path.resolve(path.normalize(p));
+  // If the original was a UNC path but normalization lost the prefix, restore it
+  if (isUNC && !normalized.startsWith('\\\\')) {
+    normalized = '\\' + normalized;
+  }
+  return normalized;
+}
+
 /**
  * Checks if an absolute path is within any of the allowed directories.
  * 
@@ -27,14 +43,14 @@
   // Normalize the input path
   let normalizedPath: string;
   try {
-    normalizedPath = path.resolve(path.normalize(absolutePath));
+    normalizedPath = safeNormalize(absolutePath);
   } catch {
     return false;
   }
 
   // Verify it's absolute after normalization
   if (!path.isAbsolute(normalizedPath)) {
     throw new Error('Path must be absolute after normalization');
   }
 
   // Check against each allowed directory
@@ -51,7 +67,7 @@
     // Normalize the allowed directory
     let normalizedDir: string;
     try {
-      normalizedDir = path.resolve(path.normalize(dir));
+      normalizedDir = safeNormalize(dir);
     } catch {
       return false;
     }