diff --git a/src/linker.rs b/src/linker.rs
index e8855ba5..dc0b0286 100644
--- a/src/linker.rs
+++ b/src/linker.rs
@@ -388,6 +388,15 @@ impl Linker {
 
                 // For NestedGlob, `source` is relative to the project root (not source_dir).
                 let search_root = self.project_root.join(&target.source);
+                // SECURITY: Validate search root to prevent traversal/absolute escapes.
+                self.revalidate_destination_path(&search_root)
+                    .with_context(|| {
+                        format!(
+                            "NestedGlob source resolves outside project root: {}",
+                            target.source
+                        )
+                    })?;
+
                 self.process_nested_glob(
                     &search_root,
                     target.pattern.as_deref().unwrap_or("**/AGENTS.md"),
@@ -1150,6 +1159,10 @@ impl Linker {
 
                         // Re-discover the same files and remove the corresponding symlinks.
                         let search_root = self.project_root.join(&target_config.source);
+                        // SECURITY: Validate search root to prevent traversal/absolute escapes.
+                        if self.revalidate_destination_path(&search_root).is_err() {
+                            continue;
+                        }
                         if !search_root.exists() || !search_root.is_dir() {
                             continue;
                         }
diff --git a/tests/test_security.rs b/tests/test_security.rs
new file mode 100644
index 00000000..27611341
--- /dev/null
+++ b/tests/test_security.rs
@@ -0,0 +1,94 @@
+use agentsync::config::Config;
+use agentsync::linker::{Linker, SyncOptions};
+use std::fs;
+use tempfile::TempDir;
+
+#[test]
+fn test_nested_glob_search_root_traversal() {
+    let temp_dir = TempDir::new().unwrap();
+    let project_root = temp_dir.path().join("project");
+    let agents_dir = project_root.join(".agents");
+    fs::create_dir_all(&agents_dir).unwrap();
+
+    // Create a file OUTSIDE the project root
+    let outside_dir = temp_dir.path().join("outside_dir");
+    fs::create_dir_all(&outside_dir).unwrap();
+    fs::write(outside_dir.join("AGENTS.md"), "outside").unwrap();
+
+    let config_path = agents_dir.join("agentsync.toml");
+
+    // We want to walk a directory OUTSIDE the project root
+    let relative_outside = "../outside_dir";
+
+    let toml = format!(
+        r#"
+        source_dir = "."
+        [agents.malicious]
+        enabled = true
+        [agents.malicious.targets.nested]
+        source = "{}"
+        destination = "leaked/{{file_name}}"
+        type = "nested-glob"
+    "#,
+        relative_outside
+    );
+
+    fs::write(&config_path, toml).unwrap();
+
+    let config = Config::load(&config_path).unwrap();
+    let linker = Linker::new(config, config_path.clone());
+
+    let options = SyncOptions {
+        verbose: true,
+        ..Default::default()
+    };
+    let result = linker.sync(&options).unwrap();
+
+    // The target should have failed due to unsafe search root
+    assert!(
+        result.errors > 0,
+        "Sync should have errors for malicious search root"
+    );
+
+    let leaked_link = project_root.join("leaked").join("AGENTS.md");
+    assert!(
+        !leaked_link.exists(),
+        "Should NOT have created a symlink to a file discovered outside project root"
+    );
+    assert!(
+        !project_root.join("leaked").exists(),
+        "Should NOT have created the leaked directory"
+    );
+
+    // Absolute paths should also be rejected.
+    // Use replace to escape backslashes so the path is valid in a TOML basic string on Windows.
+    let path_str = outside_dir.display().to_string().replace('\\', "\\\\");
+    let absolute_toml = format!(
+        r#"
+        source_dir = "."
+        [agents.malicious]
+        enabled = true
+        [agents.malicious.targets.nested]
+        source = "{}"
+        destination = "leaked/{{file_name}}"
+        type = "nested-glob"
+    "#,
+        path_str
+    );
+    fs::write(&config_path, absolute_toml).unwrap();
+
+    let absolute_config = Config::load(&config_path).unwrap();
+    let absolute_linker = Linker::new(absolute_config, config_path);
+    let absolute_result = absolute_linker.sync(&options).unwrap();
+    assert!(
+        absolute_result.errors > 0,
+        "Sync should have errors for absolute-path search root"
+    );
+
+    // clean() must not traverse or remove anything outside the project.
+    let clean_result = absolute_linker.clean(&SyncOptions::default()).unwrap();
+    assert_eq!(
+        clean_result.removed, 0,
+        "Clean should not remove anything for an invalid search root"
+    );
+}