openvas - Man Page

The Scanner of the Greenbone Vulnerability Management

Synopsis

openvas [-v] [-h]  [-c config-file] [--scan-start scan-uuid] [-u] [-s] [-y]

Description

Greenbone Vulnerability Management (GVM) is a vulnerability auditing and management framework made up of several modules. The OpenVAS Scanner, openvas is in charge of executing many security tests against many target hosts in a highly optimized way.

openvas inspects the remote hosts to list all the vulnerabilities and common misconfigurations that affects them.

It is a command line tool with parameters to update the feed of vulnerability tests and to start a scan. The second part of the interface is the redis store where the parameters about a scan task need to be placed and from where the results can be retrieved.

Options

-c <config-file>, --config-file=<config-file>

Use the alternate configuration file instead of /etc/openvas/openvas.conf

-v, --version

Prints the version number and exits

-h, --help

Show a summary of the commands

--scan-start=<scan-uuid>

ID for a single scan task. The scanner will start the scan with the data already loaded in a redis KB, which will be found using the given scan-id.

--scan-stop=<scan-uuid>

ID for a single scan task. The scanner will search the redis kb associated to the given scan_id. It takes the pid from the kb and sends the SIGUSR2 kill signal to stop the scan.

-u, --update-vt-info

Updates VT info into redis store from VT files.

The Configuration File

The default openvas configuration file, /etc/openvas/openvas.conf contains these options:

plugins_folder

Contains the location of the plugins folder. This is usually /var/lib/openvas/plugins, but you may change this.

max_hosts

is maximum number of hosts to test at the same time which should be given to the client (which can override it). This value must be computed given your bandwidth, the number of hosts you want to test, your amount of memory and the horsepower of your processor(s).

max_checks

is the number of plugins that will run against each host being tested. Note that the total number of process will be max_checks x max_hosts so you need to find a balance between these two options. Note that launching too many plugins at the same time may disable the remote host, either temporarily (ie: inetd closes its ports) or definitely (the remote host crash because it is asked to do too many things at the same time), so be careful.

log_whole_attack

If this option is set to 'yes', openvas will store the name, pid, date and target of each plugin launched. This is helpful for monitoring and debugging purpose, however this option might make openvas fill your disk rather quickly.

log_plugins_name_at_load

If this option is set to 'yes', openvas will log the name of each plugin being loaded at startup, or each time it receives the HUP signal.

cgi_path

By default, openvas looks for default CGIs in /cgi-bin and /scripts. You may change these to something else to reflect the policy of your site. The syntax of this option is the same as the shell $PATH variable: path1:path2:...

port_range

This is the default range of ports that the scanner plugins will probe. The syntax of this option is flexible, it can be a single range ("1-1500"), several ports ("21,23,80"), several ranges of ports ("1-1500,32000-33000"). Note that you can specify UDP and TCP ports by prefixing each range by T or U. For instance, the following range will make openvas scan UDP ports 1 to 1024 and TCP ports 1 to 65535 : "T:1-65535,U:1-1024".

optimize_test

By default, openvas does not trust the remote host banners. It means that it will check a webserver claiming to be IIS for Apache flaws, and so on. This behavior might generate false positive and will slow the scan down somehow. If you are sure the banners of the remote host have not been tampered with, you can safely enable this option, which will force the plugins to perform their job only against the services they have been designed to check.

test_empty_vhost

If set to yes, the scanner will also test the target by using empty vhost value in addition to the target's associated vhost values.

checks_read_timeout

Number of seconds that the security checks will wait for when doing a recv(). You should increase this value if you are running openvas across a slow network slink (testing a host via a dialup connection for instance)

timeout_retry

Number of retries when a socket connection attempt timesout.

open_sock_max_attempts

When a port  is found as opened at the beginning of the scan, and for some reason the status changes to filtered/closed, it will not be possible to open a socket. This is the number of unsuccessful retries to open the socket before to set the port as closed. This avoids to launch plugins which need the opened port as a mandatory key, therefore it avoids an overlong scan duration. If the set value is 0 or a negative value, this option is disabled. It should be take in account that one unsuccessful attempt needs the number of retries set in "timeout_retry".

time_between_request

Some devices do not appreciate quick connection establishment and termination neither quick request. This option allows you to set a wait time between two actions like to open a tcp socket, to send a request through the open tcp socket, and to close the tcp socket. This value should be given in milliseconds. If the set value is 0 (default value), this option is disabled and there is no wait time between requests.

expand_vhosts

Whether to expand the target host's list of vhosts with values gathered from sources such as reverse-lookup queries and VT checks for SSL/TLS certificates.

non_simult_ports

Some services (in particular SMB) do not appreciate multiple connections at the same time coming from the same host. This option allows you to prevent openvas to make two connections on the same given ports at the same time. The syntax of this option is "port1[, port2....]". Note that you can use the KB notation of openvas to designate a service formally. Ex: "139, Services/www", will prevent openvas from making two connections at the same time on port 139 and on every port which hosts a web server.

plugins_timeout

This is the maximum lifetime, in seconds of a plugin. It may happen that some plugins are slow because of the way they are written or the way the remote server behaves. This option allows you to make sure your scan is never caught in an endless loop because of a non-finishing plugin. Doesn't affect ACT_SCANNER plugins.

scanner_plugins_timeout

Like plugins_timeout, but for ACT_SCANNER plugins.

safe_checks

Most of the time, openvas attempts to reproduce an exceptional condition to determine if the remote services are vulnerable to certain flaws. This includes the reproduction of buffer overflows or format strings, which may make the remote server crash. If you set this option to 'yes', openvas will disable the plugins which have the potential to crash the remote services, and will at the same time make several checks rely on the banner of the service tested instead of its behavior towards a certain input. This reduces false positives and makes openvas nicer towards your network, however this may make you miss important vulnerabilities (as a vulnerability affecting a given service may also affect another one).

auto_enable_dependencies

OpenVAS plugins use the result of each other to execute their job. For instance, a plugin which logs into the remote SMB registry will need the results of the plugin which finds the SMB name of the remote host and the results of the plugin which attempts to log into the remote host. If you want to only select a subset of the plugins available, tracking the dependencies can quickly become tiresome. If you set this option to 'yes', openvas will automatically enable the plugins that are depended on.

source_iface

Name of the network interface that will be used as the source of connections established by OpenVAS. The scan won't be launched if the value isn't authorized according to (sys_)ifaces_allow / (sys_)ifaces_deny if present.

ifaces_allow

Comma-separated list of interfaces names that are authorized as source_iface values.

ifaces_deny

Comma-separated list of interfaces names that are not authorized as source_iface values.

sys_ifaces_allow

Like ifaces_allow. Can't be overridden by the client.

sys_ifaces_deny

Like ifaces_deny. Can't be overridden by the client.

hosts_allow

Comma-separated list of the only targets that are authorized to be scanned. Supports the same syntax as the list targets. Both target hostnames and the address to which they resolve are checked. Hostnames in hosts_allow list are not resolved however.

hosts_deny

Comma-separated list of targets that are not authorized to be scanned. Supports the same syntax as the list targets. Both target hostnames and the address to which they resolve are checked. Hostnames in hosts_deny list are not resolved however.

sys_hosts_allow

Like hosts_allow. Can't be overridden by the client.

sys_hosts_deny

Like hosts_deny. Can't be overridden by the client.

The other options in this file can usually be redefined by the client.

Network Usage

Bear in mind that OpenVAS can be quite network intensive. Even if the OpenVAS developers have taken every effort to avoid packet loss (including transparently resending UDP packets, waiting for data to be received in TCP connections, etc.) so bandwidth use should always be closely monitored,  with current server hardware, bandwidth is usually the bottleneck in  a OpenVAS scan. It might not became too apparent in the final reports, scanners will still run, holes might be detected, but you will risk to run into false negatives (i.e. OpenVAS will not report a security hole that is present in a remote host)

Users might need to tune OpenVAS configuration if running the scanner in low bandwidth conditions (low being 'less bandwidth that the one your hardware system can produce) or otherwise will get erratic results. There are several parameters that can be modified to reduce network load:

checks_read_timeout

The default value is set to 5 seconds, that can (should) be increased if network bandwidth is low in the openvas.conf or openvasrc configuration files. Notice that it is recommended to increase this this value, if you are running a test outside your LAN  (i.e. to Internet hosts through an Internet connection), to over 10 seconds.

max_hosts

Number of hosts to test at the same time. It can be as low as you want it to be (obviously 1 is the minimum)

max_checks

Number of checks to test at the same time it can be as low as you want it to be and it will also reduce network load and improve performance (obviously 1 is the minimum) Notice that OpenVAS will spawn max_hosts * max_checks processes.

vendor_version

Use the alternate vendor instead of the default one during scans.

Other options might be using the QoS features offered by your server operating system or your network to improve the bandwidth use.

It is not easy to give a bandwidth estimate for a OpenVAS run, you will probably need to make your own counts. However, assuming you test 65536  TCP ports. This will require at least a single packet per port that is  at least 40 bytes large. Add 14 bytes for the ethernet header and you  will send 65536 * (40 + 14) = 3670016 bytes. So for just probing all TCP ports we may need a multitude of this as nmap will try to resend the packets twice if no response is received.

A very rough estimate is that a full scan for UDP, TCP and RPC as well as  all NASL scripts may result in 8 to 32 MB worth of traffic per scanned host.  Reducing the amount of tested part and such will reduce the amount of data to be transferred significantly.

MORE INFORMATION ABOUT Greenbone Vulnerability Management

The canonical places where you will find more information  about OpenVAS are:

https://community.greenbone.net (Community site)
https://github.com/greenbone/ (Development site)
https://www.openvas.org/ (Traditional home site)

Authors

openvas was forked from nessusd in 2005. Nessusd was written by Renaud Deraison <deraison@cvs.nessus.org>. Most new code since 2005 developed by Greenbone Networks GmbH.

Referenced By

greenbone-nvt-sync(8), openvas-nasl(1).

June 2019 Greenbone Vulnerability Management User Manuals