Censys Internet Scanning Intro
Host Scanning Introduction
What Does Censys Scan?
Censys continually scans the entire public IPv4 address space on 3,592+ ports using automatic protocol detection to present the most accurate representation of the Internet’s current state.
Censys also leverages redirects and the Domain Name System to discover and scan (~79M) in-use IPv6 addresses.
Censys scans only obtain information: Censys never attempts to log into any service, read any database, or otherwise gain authenticated access to any system.
How Often Does Censys Scan For New Services?
Discovery means finding a service on an IP/port that was not there last time we looked. Censys has several schedules for discovery based on our experience scanning the Internet:
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Global Scan of Popular Ports. We scan the whole IPv4 space on 137 ports with IANA-assigned services every day.
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Cloud Provider Scans. Since many cloud hosts are ephemeral, we scan the 1,440 most popular ports on Amazon, Google, and Azure hosts every day.
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Global Scan of Less Popular Ports. We scan the whole IPv4 space on 3,455 additional ports on a regular basis, completing a walk every 10 days.
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Global Scan of Every Other Port Number. We scan the entire IPv4 address space across ALL ports (65535) at a low background rate.
How Often Does Censys Refresh Data for Known Services?
Once a service has been discovered, Censys prioritizes refreshing the information about that service to ensure it is accurate and up to date.
Once a day, the age of each of the ~2.1 Billion services in our data set is checked. Any (unnammed) service with an observation timestamp older than 24 hours is rescanned. With this process, the average age of high-value service data is about 16 hours!
How Does Censys Scan?
Censys has invested time and technology into setting up multiple global perspectives and developing sophisticated scanning techniques to produce the richest, most useful data set for the security community.
Global Scanning Perspectives
Censys peers with and scans from five Tier-1 ISPs (NTT, Tata, Hurricane Electric, Telia, Orange) to produce nearly 99% coverage of listening hosts across the globe with enhanced protection against packet drop.
The ISP that Censys scanned any given service from is recorded in the services.perspective field.
Deep Protocol Scans
On ports with IANA-assigned protocols, Censys attempts to complete a handshake with the assigned protocol (e.g., Telnet on port 23). If that fails, we try additional handshakes according to our experience with protocol and port pairings. On ports without an assigned service, we start by sending an HTTP request and attempt to automatically detect the protocol based on the response.
The Censys scanner analyzes every server response to identify its service, even if it’s non-standard for the port, which allows us to uncover the vast majority of services in unexpected places.
For example, if an HTTP request results in an SSH banner, Censys will close the HTTP connection and reattempt an SSH handshake.
Censys can detect 25 protocols on any port. They are indicated in the list below with a (1).
Lightweight Protocol Scans
Some protocols do not have a lot of data to parse and index.
Censys identifies 47 lightweight services and collects a banner. They are indicated in list below with a (2).
What Protocols (Services) Does Censys Detect?
Censys can detect and complete scans for over 100 Layer 7 protocols. The default Layer 4 protocol used by our scanners is TCP, although some protocols, such as DNS, are scanned with UDP, and HTTP can be detected over QUIC.
Service names represent the most specific service information we have.
For example, a generic HTTP service has a service name of HTTP, while an HTTP service that’s actually an Elasticsearch server has a service name of ELASTICSEARCH.
There is also an UNKNOWN fallback, which means that Censys could not identify the protocol in use by an open service, either because the service is not adhering to a protocol (there are a lot of HTTP-like services in there) or because Censys does not have a protocol-specific scanner written.
The list below is provided for informational purposes only. For programmatic integration, users should rely on the always up-to-date list of all protocols available via API.
AMQP (1) ANDROMOUSE (2) ANYCONNECT (1) ARD (2) ATG (2) BACNET BEANSTALKD BGP (1) BITCOIN BITTORRENT (2) BITTORRENT_TRACKER BOLT (2) CASSANDRA (1) (2) CHARGEN (2) CITRIX (2) COAP CODESYS (2) CWMP DB2 (2) DICT DIGI (2) DNP3 DNS EIP ELASTICSEARCH (1) FINS FORTIGATE FORTIGUARD FOX FTP (1) GE_SRTP (2) HART HTTP (1) ICAP (2) IDENT (2) IEC60870_5_104 (2) IKE IMAP (1) IPMI IPP (1) IRC (2) KAFKA KERBEROS KUBERNETES (1) LDAP (1) (2) MDNS (2) MEMCACHED MIKROTIK_BW (2) MMS MODBUS (1) MONGODB (1) MQTT MSSQL MURMUR (2) MYSQL (1) NATPMP (2) NETBIOS (2) NETIS (2) NTP OPENVPN ORACLE PCWORX (2) PC_ANYWHERE PIGEONHOLE (2) PJL (2) POP3 (1) POPPASSD (2) PORTMAP (2) POSTGRES PPTP (1) PROMETHEUS (1) PRO_CON_OS (2) QOTD (2) RADIUS RDP (1) REDIS (1) RETHINKDB (2) RIPV1 (2) RSYNC (2) RTSP (2) S7 SCCM SENTINEL (2) SIP (1) SKINNY SLP SMB SMTP (1) SNMP SSDP (2) SSH (1) STATSD TEAMSPEAK (2) TEAM_VIEWER TELNET (1) TERRARIA (2) TFTP (2) TORCONTROL (2) UBIQUITI (2) UNKNOWN UPNP (1) (2) VALVE (2) VNC (1) WDBRPC (2) WS_DISCOVERY (2) X11 XDMCP (2) XMPP ZOOKEEPER
| 1 | Censys can detect these protocols on any port number. |
| 2 | These are lightweight protocols whose only scan data is a banner. |
More information about our data collection by protocol category is provided below.
HTTP + HTTPS
On ports running HTTP(S), we request the root (/) page and follow local HTTP redirects. In addition, we perform follow-up requests to identify and classify HTTP applications.
Databases
We check for popular database servers. We never attempt to authenticate against databases or read any user databases.
Core Internet Protocols
On ports running protocols that find and coordinate services on the internet, Censys completes a protocol-specific handshake or collects the banner
Internet of Things Protocols
On ports running message broker protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate. For (MQTT) services not requiring authentication that are broadcasting messages, we may collect a sample of these messages.
Remote Access Protocols
Upon detection of remote access protocols, Censys never attempts to authenticate and never collects any screenshots, even if the functionality is enabled with no credential requirements.
Mail Protocols
On ports running common mail protocols, we collect banner data and complete a STARTTLS handshake if the server indicates support.
VoIP Protocols
On ports running common VoIP protocols, we collect banner data and complete a STARTTLS handshake if the server indicates support.
Network Administration Protocols
On ports running network administration protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate.
File-Sharing Protocols
On ports running file-sharing protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate.
Industrial Control (SCADA) Protocols
On ports running industrial control protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate.
What Ports Does Censys Scan?
Censys continually connects to Internet hosts on more than 3500 ports as part of scheduled discovery scans.
HTTP redirects may result in scans of port numbers not listed in the appendix.
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