The Nmap hosted security tool can help you determine how well your firewall and security configuration is working. This guide will show you how to use Nmap to scan all open ports on Linux systems.
Different kinds of services use different ports by default. For example, regular web traffic uses port 80, while the POP3 email uses port One of the ways that a firewall works is by allowing or restricting traffic over a particular port. If you need assistance with installing Nmap, refer to our tutorial on How to Install Nmap on Linux systems.
This is the basic format for Nmapand it will return information about the ports on that system. In addition to scanning by IP address, you can also use the following commands to specify a target:. Note: The developers at nmap. You can use this to test your Nmap utility. Nmap commands can be used to scan a single port or a series of ports:. Run a fast scan on the target system, but bypass host discovery. Host discovery uses pingbut many server firewalls do not respond to ping requests.
This option forces the test without waiting for a reply that may not be coming :. The nmap utility can be used to detect the operating system of a particular target:. Note: The —sV option can be tuned to be more or less aggressive in its scan.
Use the ——version-intensity 2 option to specify the level of testing.
Replace the number 2 with a number from 0 light testing to 9 run all probes. The more intense the testing, the longer the scan will take. A Linux firewall can be configured to block all traffic on a particular port. You can use firewall rules to allow some ports, but block others. Use a firewall in conjunction with other network security tools and software to scan traffic on a particular port, and to watch for suspicious traffic.
You should only use Nmap port scanning on servers that you own, or that you have permission to scan. Often, port-scanning is seen as an aggressive method, or a prelude to a cyber attack. It is possible that during your scan, you may find unusual activity. For example, you may see a service running on an unusual port number.
This means there is something strange going on, and should be investigated. The OS and Service scanning options are helpful for scanning a particular port or service to get more information. If a service is running on a non-default port, it might be by design — or it might suggest there is a security breach. Ports often have a default usage.Switches IOS version is There is a known bugID for this. You should upgrade to one of the IOS versions that fixes the vulnerability. I am getting this vulnerability flagged by Nessus on a X running Yet the CSCum bug description claims that it is fixed as of At this point I don't know if it is Nessus or the bug description that is in error.
Morning again. Also, would ntp allow mode private work as well. I've been digging hard to find a way to remediate this.
How to detect NTP Amplification DoS Attacks
I have a customer that presented to us a scan of network devices vulnerable to this bug. It had several items in the list. I had opened a TAC case and was advised to apply the "ntp allow mode control 3" command. I was only able to apply this command to one device. However, the "mode control 3" command did eliminate this device from my customer's vulnerability scan. The other devices had an "ntp allow mode private" command, but no "ntp allow mode control".
I further engaged Cisco and they claimed that the IOS versions that I provided them, for the remaining devices, were not affected by the NTP mode 6 scanner vulnerability. Although, the remaining devices still surface on my customer's NTP mode 6 scan. These are the 4 IOS versions that currently do not support the "ntp allow mode control" command: cipbasek9-mz. Can anyone help me determine which next up-version for each of these platforms, supports the "ntp allow mode control" command?
Buy or Renew. Find A Community. Cisco Community. Turn on suggestions.We just had an internal security scan run and the Nessus software found this vulnerability on our Juniper EX switches running Junos We do point all of our Juniper switches to our internal ntp server via this command.
Can I somehow fix this so these switches do not respond to this NTP query? We do sit behind a firewall that should mitigate that ability for someone to run an attack but I still thing it is important to rectify this issue.
You should also ask them to include in next We had the same internal security audit run last year and the same vulnerability was identified. I did not pursue it at that point since the Nessus software identified quite a few other problems we did work on. So what you are saying is this issue has existed for awhile and Juniper has just not addressed it in Junos to date? A quick search brings up this link:. From looking at this, it appears EX not affected? I would still think this type of situation should be work at least in parallel with TAC.
They pointed me to this. For example:. This term may be added to the existing loopback interface filter as part of an overall control plane protection strategy. I have been doing a lot of reading about how to protect against an NTP deflection attack.
Network Time Protocol
Nearly all of it talks about protecting the routing engine and applying some type of firewall filter to the loopback port. All of my edge switches are EX that are strictly layer 2. All of the routing happens at the core. What I am not sure of is how to setup a firewall filter for ntp traffic for these edge switches. The firewall filters are applied to the layer 3 interface where you have the mgmt address for the switch configured.
This is the address where traffic for the routing engine is processed. Once the filter is in place only the authorized ntp traffic is accepted on the mgmt address for the switch itself. Ethernet Switching.Each record contains information about the most recent NTP packet sent by a host to the target including the source and destination addresses and the NTP version and mode of the packet.
With this information it is possible to classify associated hosts as Servers, Peers, and Clients. A Peers command is also sent to the target and the peers list in the response allows differentiation between configured Mode 1 Peers and clients which act like Peers such as the Windows W32Time service. Associated hosts are further classified as either public or private.
Private hosts are those having IP addresses which are not routable on the public Internet and thus can help to form a picture about the topology of the private network on which the target resides.
Other information revealed by the monlist and peers commands are the host with which the target clock is synchronized and hosts which send Control Mode 6 and Private Mode 7 commands to the target and which may be used by admins for the NTP service. It should be noted that the very nature of the NTP monitor data means that the Mode 7 commands sent by this script are recorded by the target and will often appear in these results.
Since the monitor data is a MRU list, it is probable that you can overwrite the record of the Mode 7 command by sending an innocuous looking Client Mode request. Notes: The monitor list in response to the monlist command is limited to associations. The monitor capability may not be enabled on the target in which case you may receive an error number 4 No Data Available. There may be a restriction on who can perform Mode 7 commands e. This script does not handle authenticating and targets expecting auth info may respond with error number 3 Format Error.
Send an NTPv2 Mode 7 'monlist' command to the target, receive any responses and parse records from those responses. If the target responds favourably then send a 'peers' command and parse the responses. Finally, categorise the discovered NTP associations hosts and output the interpreted results.An attacker could exploit this vulnerability by sending Mode 6 control requests to NTP servers and clients and observing responses amplified up to 40 times in size.
An exploit could allow the attacker to cause a Denial of Service DoS condition where the affected NTP server is forced to process and respond with larger response data. In order to elicit significantly big response and exploit this vulnerability, an attacker would have to send a huge number of mode 6 messages to a large number of servers or clients.
All versions prior to the fix of CSCum are subject to contributing to amplification attacks via mode 6 packets.
Once CSCum is integrated you can see that via the fixed field in Bug Search Toolkityour device has access to the configuration command:. To see if a device is configured with NTP, log into the device and issue the CLI command show running-config include ntp.
If the output returns either of the following commands listed then the device is vulnerable: ntp master ntp peer ntp server ntp broadcast client ntp multicast client The following example identifies a Cisco device that is configured with NTP: router show running-config include ntp ntp peer Workaround: There are no solid workarounds other than disabling NTP on the device.
The following mitigations have been identified for this vulnerability; only packets destined for any configured IP address on the device can exploit this vulnerability.
Transit traffic will not exploit this vulnerability. Note: NTP peer authentication is not a workaround and is still a vulnerable configuration.
Additionally, ''serve-only'' keyword added to the NTP access-group will limit the exposure of the server to only respond to valid queries. Unicast RPF should be considered to be used in conjunction to offer a better mitigation solution. Although it is often difficult to block traffic that transits a network, it is possible to identify traffic that should never be allowed to target infrastructure devices and block that traffic at the border of networks.
Infrastructure ACLs iACLs are a network security best practice and should be considered as a long-term addition to good network security as well as a workaround for this specific vulnerability. The white paper entitled ''Protecting Your Core: Infrastructure Protection Access Control Lists'' presents guidelines and recommended deployment techniques for infrastructure protection access lists and is available at the following link:.
Warning: Because the feature in this vulnerability utilizes UDP as a transport, it is possible to spoof the sender's IP address, which may defeat ACLs that permit communication to these ports from trusted IP addresses.
CoPP can be configured on a device to help protect the management and control planes and minimize the risk and effectiveness of direct infrastructure attacks by explicitly permitting only authorized traffic that is sent to infrastructure devices in accordance with existing security policies and configurations.
Note: Since the NTP Amplification DoS attacks rely on sending relatively small amount of NTP requests in order to solicit large, amplified responses from the server, this workaround has only limited application.
While the requests are small, the response can grow up to 40 times in amplification factor size. Known Fixed Releases: 30 Buy or Renew. Find A Community. Cisco Community. Turn on suggestions. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
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Network Time Protocol
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Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Git stats 2 commits. Failed to load latest commit information. View code. Releases No releases published.Description: The remote NTP server responds to mode 6 queries.
Devices that respond to these queries have the potential to be used in NTP amplification attacks. Attacker would have to send a massive amount of mode 6 messages to a huge number of recipient servers or clients in your organization.
Impact: An unauthenticated, remote attacker could potentially exploit this, via a specially crafted mode 6 query, to cause a reflected denial of service condition. If access restrictions are in place, you will need to ensure that you allow time synchronization with the following command. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account.
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The key motivation behind The NetSec Addict is to deliver the determinations of network and security complications in support articles. Create a free website or blog at WordPress. Solution: Notes for Cisco IOS Catalyst Switch devices: Authenticated NTP time updates can be configured on Cisco Catalyst Switch devices with the following commands: ntp authenticate ntp authentication-key key-num md5 key-string ntp server ip-address key key-num [prefer] If access restrictions are in place, you will need to ensure that you allow time synchronization with the following command ntp access-group peer acl.
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