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 (~39M) 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 the following 25 protocols on any port:
AMQP ANYCONNECT BGP CASSANDRA ELASTICSEARCH FTP HTTP IMAP IPP KUBERNETES LDAP MODBUS MONGODB MYSQL POP3 PPTP PROMETHEUS RDP REDIS SIP SMTP SSH TELNET UPNP VNC
Lightweight Protocol Scans
Some protocols do not have a lot of data to parse and index.
Censys identifies the following lightweight services and collects a banner:
ANDROMOUSE ARD ATG BEANSTALKD BITTORRENT BOLT CASSANDRA CHARGEN CITRIX CODESYS DB2 DIGI GE_SRTP ICAP IDENT IEC60870_5_104 IRC LDAP MDNS MIKROTIK_BW MURMUR NATPMP NETBIOS NETIS PCWORX PIGEONHOLE PJL POPPASSD PORTMAP PRO_CON_OS QOTD RDP_UDP RETHINKDB RIPV1 RSYNC RTSP SENTINEL SSDP TEAMSPEAK TERRARIA TFTP TORCONTROL UBIQUITI UPNP VALVE WDBRPC WS_DISCOVERY XDMCP
What Protocols (Services) Does Censys Detect?
Censys can detect 105 Layer 7 protocols. The default Layer 4 protocol is TCP, although some protocols, such as DNS, are scanned with UDP, and HTTP can be detected on QUIC.
In addition, we perform several HTTP(S) handshakes to identify specific HTTP applications (e.g., Kubernetes and Elasticsearch). 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.
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 the following applications:
CWMP Elasticsearch Kubernetes Prometheus
Databases
We check for the following popular database servers. We never attempt to authenticate against databases or read any user databases.
Bolt Cassandra Elasticsearch Memcached MongoDB Microsoft SQL Server (MSSQL) MySQL Oracle PostgreSQL Redis RethinkDB IBM DB2 Zookeeper Core Internet Protocols DNS Open Resolvers Multicast DNS (MDNS) ECHO IPP ICAP NETBIOS NTP PORTMAP NATPMP RIPV1
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.
AMQP(S) COAP(S) MQTT(S) BEANSTALKD IKETTLE KAFKA NETIS PJL Ubiquity Discovery Protocol (UBIQUITI) SSDP UPNP Web Services Dynamic Discovery (WS_DISCOVERY) XMPP
Remote Access Protocols
We check for the following remote access protocols.
Andromouse OpenVPN PC Anywhere RDP RDP_UDP SSH Telnet VNC X11 XDMCP Apple Remote Desktop (ARD) TEAM_VIEWER
Mail Protocols
On ports running common mail protocols, banner data is collected and a STARTTLS handshake is completed if the server indicates support.
IMAP(S) PIGEONHOLE POP3(S) SMTP(S)
VoIP Protocols
On ports running common VoIP protocols, banner data is collected and a STARTTLS handshake is completed if the server indicates support.
SIP(S) SKINNY MURMUR TEAMSPEAK
Network Administration Protocols
On ports running network administration protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate.
IPMI Kerberos LDAP POPPASSED PPTP RADIUS SCCM SNMP Sentinel License Manager (SENTINEL) TORCONTROL
File-Sharing Protocols
On ports running file-sharing protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate.
BITTORRENT BITTORRENT_TRACKER FTP(S) RSYNC SMB TFTP
Industrial Control (SCADA) Protocols
On ports running industrial control protocols, we complete an initial protocol-specific handshake, with no attempt to authenticate.
Automated Tank Gauges (ATG) BACnet DNP3 EIP FINS HART Tridium Fox (FOX) MODBUS Siemens S7 CODESYS Digi Realport (DIGI) Service Request Transport Protocol (GE_SRTP) Citrix ICA Protocol (CITRIX) PCWORX IEC_60870_5_104 ProConOS (PRO_CON_OS) VxWorks WDB Debug Agent (WDBRPC)
Gaming Protocols
RTSP Source Engine Server (VALVE) Terraria Server (TERRARIA)
Miscellaneous Protocols
BITCOIN CHARGEN DICT IDENT IRC Quote of the Day (QOTD) STATSD
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 ports not listed in the appendix.
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