  shell(chan, wantReply) {
    if (this._server)
      throw new Error('Client-only method called in server mode');

    // Does not consume window space

    let p = this._packetRW.write.allocStart;
    const packet = this._packetRW.write.alloc(1 + 4 + 4 + 5 + 1);

    packet[p] = MESSAGE.CHANNEL_REQUEST;

    writeUInt32BE(packet, chan, ++p);

    writeUInt32BE(packet, 5, p += 4);
    packet.utf8Write('shell', p += 4, 5);

    packet[p += 5] = (wantReply === undefined || wantReply === true ? 1 : 0);

    this._debug
      && this._debug(`Outbound: Sending CHANNEL_REQUEST (r:${chan}, shell)`);
    sendPacket(this, this._packetRW.write.finalize(packet));
  }
The software constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.