Advanced Settings in Vulnerability Management Scans

Note: If a scan is based on a user-defined template, you cannot configure Advanced settings in the scan. You can only modify these settings in the related user-defined template.

The Advanced settings provide increased control over scan efficiency and the operations of a scan, as well as the ability to enable plugin debugging.

Certain Tenable-provided scanner templates include preconfigured advanced settings.

If you select the Custom preconfigured setting option, or if you are using a scanner template that does not include preconfigured advanced settings, you can manually configure Advanced settings in the following categories:

Note: The following tables include settings for the Advanced Network Scan template. Depending on the template you select, certain settings may not be available, and default values may vary.

Setting Default Value Description
General Settings
Enable Safe Checks Enabled

When enabled, disables all plugins that may have an adverse effect on the remote host.

Stop scanning hosts that become unresponsive during the scan Disabled

When enabled, Tenable.io stops scanning if it detects that the host has become unresponsive. This may occur if users turn off their PCs during a scan, a host has stopped responding after a denial of service plugin, or a security mechanism (for example, an IDS) has started to block traffic to a server. Normally, continuing scans on these machines sends unnecessary traffic across the network and delay the scan.

Scan IP addresses in a random order Disabled

By default, Tenable.io scans a list of IP addresses in sequential order. When this option is enabled, Tenable.io scans the list of hosts in a random order within an IP address range. This approach is typically useful in helping to distribute the network traffic during large scans.

Scan targets with multiple domain names in parallel Disabled

When disabled, to avoid overwhelming a host, Tenable.io prevents a single scanner from simultaneously scanning multiple targets that resolve to a single IP address. Instead, Tenable.io scanners serialize attempts to scan the IP address, whether it appears more than once in the same scan task or in multiple scan tasks on that scanner. Scans may take longer to complete.

When enabled, a Tenable.io scanner can simultaneously scan multiple targets that resolve to a single IP address within a single scan task or across multiple scan tasks. Scans complete more quickly, but hosts could potentially become overwhelmed, causing timeouts and incomplete results.

Automatically accept detected SSH disclaimer prompts Disabled

When enabled, if a credentialed scan tries to connect via SSH to a FortiOS host that presents a disclaimer prompt, the scanner provides the necessary text input to accept the disclaimer prompt and continue the scan.

When disabled, credentialed scans on hosts that present a disclaimer prompt fail because the scanner cannot connect to the device and accept the disclaimer. The error appears in the plugin output.

Create unique identifier on hosts scanned using credentials Enabled When enabled, the scanner creates a unique identifier for credentialed scans.
Performance Options

Slow down the scan when network congestion is detected

Disabled

When enabled, Tenable.io detects when it is sending too many packets and the network pipe is approaching capacity. If network congestion is detected, Tenable.io throttles the scan to accommodate and alleviate the congestion. Once the congestion has subsided, Tenable.io automatically attempts to use the available space within the network pipe again.

Use Linux kernel congestion detection

Disabled

When enabled, Tenable.io uses the Linux kernel to detect when it sends too many packets and the network pipe approaches capacity. If detected, Tenable.io throttles the scan to accommodate and alleviate the congestion. Once the congestion subsides, Tenable.io automatically attempts to use the available space within the network pipe again.

Network timeout (in seconds)

5

Specifies the time that Tenable.io waits for a response from a host unless otherwise specified within a plugin. If you are scanning over a slow connection, you may want to set this to a higher number of seconds.

Max simultaneous checks per host

5

Specifies the maximum number of checks a Tenable.io scanner will perform against a single host at one time.

Max simultaneous hosts per scan

depends on the Tenable-provided template used for the scan

Specifies the maximum number of hosts that a Tenable.io scanner will scan at the same time.

Max number of concurrent TCP sessions per host

none

Specifies the maximum number of established TCP sessions for a single host.

This TCP throttling option also controls the number of packets per second the SYN scanner sends, which is 10 times the number of TCP sessions. For example, if this option is set to 15, the SYN scanner sends 150 packets per second at most.

Max number of concurrent TCP sessions per scan

none

Specifies the maximum number of established TCP sessions for the entire scan, regardless of the number of hosts being scanned.

For scanners installed on any Windows host, you must set this value to 19 or less to get accurate results.

Unix Find Command Exclusions

Custom filepath

none

A plain text file containing a list of filepaths to exclude from all plugins that search using the find command on Unix systems.

In the file, enter one filepath per line, formatted per patterns allowed by the Unix find command -path argument. For more information, see the find command man page.

Custom filesystem

none

A plain text file containing a list of filesystems to exclude from all plugins that search using the find command on Unix systems.

In the file, enter one filesystem per line, using filesystem types supported by the Unix find command -fstype argument. For more information, see the find command man page.

Include Filepath none

A plain text file containing a list of filepaths to include from all plugins that search using the find command on Unix systems.

In the file, enter one filepath per line, formatted per patterns allowed by the Unix find command -path argument. For more information, see the find command man page.

Including filepaths increases the locations that are searched by plugins, which extends the duration of the scan. Make your inclusions as specific as possible.

Tip: Avoid having the same filepaths in Include Filepath and Exclude Filepath. This conflict may result in the filepath being excluded from the search, though results may vary by operating system.

Debug Settings

Enable plugin debugging

Disabled

Attaches available debug logs from plugins to the vulnerability output of this scan.

Audit Trail Verbosity Default

Controls verbosity of the plugin audit trail.

Options include:

  • No audit trail — (Default) Tenable.io does not generate a plugin audit trail.
  • All audit trail data — The audit trail includes the reason why plugins were not included in the scan.
  • Only scan errors — The audit trail includes only errors encountered during the scan.
Stagger Scan Start
Maximum delay (minutes) 0

(Agent scans only) (Agents 8.2 and later) If set, each agent in the agent group delays starting the scan for a random number of minutes, up to the specified maximum. Staggered starts can reduce the impact of agents that use a shared resource, such as virtual machine CPU.

If the maximum delay you set exceeds your scan window, Tenable.io shortens your maximum delay to ensure that agents begin scanning at least 30 minutes before the scan window closes.