NousResearch/hermes-agent · error · Error

Unsafe SSH target: host must not start with a dash ("${host}

Error message

Unsafe SSH target: host must not start with a dash ("${host}").

What it means

Thrown by validateSshTarget() when the SSH host begins with a dash. A leading dash makes argument parsers treat the value as an option flag once placed on the ssh command line, so it is rejected as an argument-injection hazard before any ssh invocation is built.

Source

Thrown at apps/desktop/electron/ssh-connection.ts:53

import net from 'node:net'
import os from 'node:os'
import path from 'node:path'

const DEFAULT_CONNECT_TIMEOUT_MS = 15_000
const DEFAULT_EXEC_TIMEOUT_MS = 20_000
const DEFAULT_FORWARD_TIMEOUT_MS = 15_000
const CONTROL_PERSIST_SECONDS = 300

// eslint-disable-next-line no-control-regex -- deliberately reject control chars in ssh targets
const _CONTROL_CHAR_RE = /[\x00-\x1f\x7f]/

function validateSshTarget(host, user, port) {
  if (!host || typeof host !== 'string') {
    throw new Error('Unsafe SSH target: host is required.')
  }

  if (host.startsWith('-')) {
    throw new Error(`Unsafe SSH target: host must not start with a dash ("${host}").`)
  }

  if (_CONTROL_CHAR_RE.test(host)) {
    throw new Error('Unsafe SSH target: host contains control characters.')
  }

  if (user && _CONTROL_CHAR_RE.test(user)) {
    throw new Error('Unsafe SSH target: user contains control characters.')
  }

  if (user && user.startsWith('-')) {
    throw new Error(`Unsafe SSH target: user must not start with a dash ("${user}").`)
  }

  const p = Number(port)

  if (!Number.isInteger(p) || p < 1 || p > 65535) {
    throw new Error(`Unsafe SSH port: ${port} (must be 1-65535).`)

View on GitHub (pinned to c896c09c42)

Solutions

1. Correct the host to a plain hostname or IP (no leading dash).
2. Validate at the settings UI: reject host fields starting with '-' before save.
3. If the user intended ssh options, use the supported dedicated fields (port, keyPath, user), never the host string.

Example fix

// before
new SshConnection({ host: '-oProxyCommand=evil', ... })

// after
new SshConnection({ host: 'example.com', port: 22, ... })

if (typeof host !== 'string' || host.length === 0 || host.startsWith('-')) {
  rejectConfig('SSH host must be a plain hostname and must not start with a dash')
}

function isDashSafe(value: unknown): value is string {
  return typeof value === 'string' && value.length > 0 && !value.startsWith('-')
}

try {
  validateSshTarget(host, user, port)
} catch (e) {
  if (e instanceof Error && e.message.includes('host must not start with a dash')) {
    // not sanitizable: reject the config entry and ask for a corrected host
    invalidateRemoteConfig('host looks like an ssh option, not a hostname')
    return
  }
  throw e
}

When it happens

Trigger: host values like '-oProxyCommand=...', '-v', or any string starting with '-'. These arise from malformed user input, a mis-parse of a combined user@host string, or a deliberately crafted config value.

Common situations: User pastes an ssh option into the host field; a config editor stores a whole ssh command line in the host field; attacker-controlled config attempting option injection through the host slot.

Related errors

• Unsafe SSH target: user must not start with a dash ("${user}
• Unsafe SSH key path: must not start with a dash ("${keyPath}
• Unsafe SSH target: host contains control characters.
• Unsafe SSH target: user contains control characters.
• Unsafe SSH key path: contains control characters.

AI-assisted analysis of NousResearch/hermes-agent@c896c09c42 (2026-08-14). Data as JSON: /api/errors/b18e6a1c1da9111d. Report an issue: GitHub.