goshs is a feature-rich single-binary file server for red teamers and developers. From 2.1.3 until 2.1.4, the sftpserver/sftpserver.go password handler used Username != "" && Password != "", so running goshs with -b 'admin:' -sftp and no -fkf left both SFTP authentication handlers unset and allowed unauthenticated file access. This issue is fixed in version 2.1.4.

Affected: Go: github.com/patrickhener/goshs/v2, Go: goshs.de/goshs/v2

## Summary

Start goshs v2.1.3 with `-b 'admin:' -sftp`. No `-fkf`. SFTP accepts connections without password. CVE-2026-40884 blocks the empty-username variant (`-b ':pass'`). The empty-password variant bypasses that fix.

## CVE-2026-40884

**CVE-2026-40884** (GHSA-c29w-qq4m-2gcv, Apr 13 2026) reported the empty-username case: `-b ':pass'` with `-sftp`. `sftpserver.go:85` uses `&&`:

```go if s.Username != "" && s.Password != "" { sshServer.PasswordHandler = func(ctx ssh.Context, password string) bool { return subtle.ConstantTimeCompare([]byte(ctx.User()), []byte(s.Username)) == 1 && subtle.ConstantTimeCompare([]byte(password), []byte(s.Password)) == 1 } } ```

Empty username → `Username != ""` false → `PasswordHandler` nil. No `-fkf` means `PublicKeyHandler` also nil. gliderlabs/ssh sees all handlers nil and sets `NoClientAuth = true`. Unauthenticated access.

Patrickhener fixed it with a sanity check at `sanity/checks.go:114-118`:

```go if opts.FTP && opts.FTPSFTPMode && strings.HasPrefix(opts.BasicAuth, ":") { logger.Fatal("When using SFTP with password authentication, the username cannot be empty. ...") } ```

`HasPrefix(":")` catches empty username. It does not catch empty password.

## Empty Password Bypass

Same `&&` at `sftpserver.go:85`. Same nil handler. Different input:

``` goshs -b 'admin:' -sftp ```

- `Username = "admin"`, `Password = ""` - `Username != "" && Password != ""` → false. Password is empty. - `PasswordHandler` not set. No `-fk…