diff --git a/codex-rs/windows-sandbox-rs/src/bin/setup_main/win.rs b/codex-rs/windows-sandbox-rs/src/bin/setup_main/win.rs
index e1146987bf..c37da06707 100644
--- a/codex-rs/windows-sandbox-rs/src/bin/setup_main/win.rs
+++ b/codex-rs/windows-sandbox-rs/src/bin/setup_main/win.rs
@@ -165,8 +165,10 @@ fn spawn_read_acl_helper(payload: &Payload, _log: &mut dyn Write) -> Result<()>
     let payload_json = serde_json::to_vec(&read_payload)?;
     let payload_b64 = BASE64.encode(payload_json);
     let exe = std::env::current_exe().context("locate setup helper")?;
+    let spawn_cwd = crate::setup::helper_spawn_dir(&payload.codex_home);
     Command::new(&exe)
         .arg(payload_b64)
+        .current_dir(spawn_cwd)
         .stdin(Stdio::null())
         .stdout(Stdio::null())
         .stderr(Stdio::null())
diff --git a/codex-rs/windows-sandbox-rs/src/setup.rs b/codex-rs/windows-sandbox-rs/src/setup.rs
index 1995c33365..0dd4e33ef5 100644
--- a/codex-rs/windows-sandbox-rs/src/setup.rs
+++ b/codex-rs/windows-sandbox-rs/src/setup.rs
@@ -226,14 +226,17 @@ fn run_setup_refresh_inner(
         }
     };
     // Refresh should never request elevation; ensure verb isn't set and we don't trigger UAC.
+    let spawn_cwd = helper_spawn_dir(request.codex_home);
     let mut cmd = Command::new(&exe);
-    cmd.arg(&b64).stdout(Stdio::null()).stderr(Stdio::null());
-    let cwd = std::env::current_dir().unwrap_or_else(|_| request.codex_home.to_path_buf());
+    cmd.arg(&b64)
+        .current_dir(&spawn_cwd)
+        .stdout(Stdio::null())
+        .stderr(Stdio::null());
     log_note(
         &format!(
             "setup refresh: spawning {} (cwd={}, payload_len={})",
             exe.display(),
-            cwd.display(),
+            spawn_cwd.display(),
             b64.len()
         ),
         Some(&sbx_dir),
@@ -242,7 +245,7 @@ fn run_setup_refresh_inner(
         let message = format!(
             "setup refresh failed to launch helper: helper={}, cwd={}, log={}, error={err}",
             exe.display(),
-            cwd.display(),
+            spawn_cwd.display(),
             log_path.display()
         );
         log_note(&format!("setup refresh: {message}"), Some(&sbx_dir));
@@ -405,6 +408,20 @@ fn gather_helper_read_roots(codex_home: &Path) -> Vec<PathBuf> {
     vec![helper_dir]
 }
 
+pub(crate) fn helper_spawn_dir(codex_home: &Path) -> PathBuf {
+    // Launch helper processes from a Codex-local directory instead of inheriting
+    // the workspace cwd, which may be a UNC-backed mount that Windows helper
+    // process creation handles poorly.
+    let helper_dir = helper_bin_dir(codex_home);
+    if std::fs::create_dir_all(&helper_dir).is_ok() {
+        return helper_dir;
+    }
+
+    let sandbox_dir = sandbox_dir(codex_home);
+    let _ = std::fs::create_dir_all(&sandbox_dir);
+    sandbox_dir
+}
+
 fn gather_full_read_roots_for_permissions(
     command_cwd: &Path,
     permissions: &ResolvedWindowsSandboxPermissions,
@@ -758,9 +775,11 @@ fn run_setup_exe(
         }
     };
 
+    let spawn_cwd = helper_spawn_dir(codex_home);
     if !needs_elevation {
         let status = Command::new(&exe)
             .arg(&payload_b64)
+            .current_dir(&spawn_cwd)
             .creation_flags(0x08000000) // CREATE_NO_WINDOW
             .stdin(Stdio::null())
             .stdout(Stdio::null())
@@ -795,12 +814,14 @@ fn run_setup_exe(
     let params = quote_arg(&payload_b64);
     let params_w = crate::winutil::to_wide(params);
     let verb_w = crate::winutil::to_wide("runas");
+    let directory_w = crate::winutil::to_wide(&spawn_cwd);
     let mut sei: SHELLEXECUTEINFOW = unsafe { std::mem::zeroed() };
     sei.cbSize = std::mem::size_of::<SHELLEXECUTEINFOW>() as u32;
     sei.fMask = SEE_MASK_NOCLOSEPROCESS;
     sei.lpVerb = verb_w.as_ptr();
     sei.lpFile = exe_w.as_ptr();
     sei.lpParameters = params_w.as_ptr();
+    sei.lpDirectory = directory_w.as_ptr();
     // Hide the window for the elevated helper.
     sei.nShow = 0; // SW_HIDE
     let ok = unsafe { ShellExecuteExW(&mut sei) };
@@ -1662,6 +1683,17 @@ mod tests {
         assert!(roots.contains(&expected));
     }
 
+    #[test]
+    fn helper_spawn_dir_uses_local_helper_directory() {
+        let tmp = TempDir::new().expect("tempdir");
+        let codex_home = tmp.path().join("codex-home");
+
+        let spawn_dir = super::helper_spawn_dir(&codex_home);
+
+        assert_eq!(spawn_dir, helper_bin_dir(&codex_home));
+        assert!(spawn_dir.is_dir(), "helper spawn dir should be created");
+    }
+
     #[test]
     fn workspace_write_roots_remain_readable() {
         let tmp = TempDir::new().expect("tempdir");