{"history":[],"article":{"id":"455f08d5-cba7-41ce-ad25-bc70cbae4cf4","title":"Character Generator Protocol","slug":"character-generator-protocol","content":":::summary\n:::\n\n# \nThe **Character Generator Protocol** (**CHARGEN**) is a service of the [Internet Protocol Suite](https://bliptext.com/articles/internet-protocol-suite) defined in in 1983 by [Jon Postel](https://bliptext.com/articles/jon-postel).\nIt is intended for testing, debugging, and measurement purposes.\nThe protocol is rarely used, as its design flaws allow for ready misuse.\nA host may connect to a server that supports the Character Generator Protocol on either [Transmission Control Protocol](https://bliptext.com/articles/transmission-control-protocol) (TCP) or [User Datagram Protocol](https://bliptext.com/articles/user-datagram-protocol) (UDP) [port number](https://bliptext.com/articles/port-number) 19.\nUpon opening a TCP connection, the server starts sending arbitrary characters to the connecting host and continues until the host closes the connection.\nIn the UDP implementation of the protocol, the server sends a UDP datagram containing a random number (between 0 and 512) of characters every time it receives a datagram from the connecting host.\nAny data received by the server is discarded.\n\n# Inetd implementation\nOn most [Unix-like](https://bliptext.com/articles/unix-like) operating systems, a CHARGEN server is built into the [inetd](https://bliptext.com/articles/inetd) or x[inetd](https://bliptext.com/articles/inetd) [daemon](https://bliptext.com/articles/daemon-computer-software).\nThe CHARGEN service is usually not enabled by default.\nIt may be enabled by adding the following lines to the file /etc/inetd.conf and telling inetd to reload its configuration:\nchargen stream tcp nowait root internal\nchargen dgram udp wait root internal\n\n# Applications\nThe CHARGEN service may be used as a source of a byte-stream for debugging TCP network code for proper bounds checking and buffer management.\nIt may also be a source of generic payload for bandwidth measurement and/or QoS fine-tuning.\nConsideration must be given if hardware compression is active, as the output from the CHARGEN service is easily and efficiently compressed.\nThis compression can cause bandwidth tests to report the size of the data after decompression, instead of the actual amount of data which passed the wire.\n\n# Sample session\nA typical CHARGEN service session looks like this: The user connects to the host using a [telnet](https://bliptext.com/articles/telnet) client.\nThe user receives a stream of [bytes](https://bliptext.com/articles/byte).\nAlthough the specific format of the output is not prescribed by, the recommended pattern (and a [de facto standard](https://bliptext.com/articles/de-facto-standard)) is shifted lines of 72 [ASCII](https://bliptext.com/articles/ascii) characters repeating.\n$ telnet localhost chargen\nTrying 127.0.0.1...\nConnected to localhost.\nEscape character is '^]'.\n!\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefg !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefgh\n\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghi $%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijk %&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijkl &'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklm '*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmn *+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmno )*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnop +,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqr ,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrs -./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrst ./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstu /0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuv 0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvw\n123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwx\n23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxy\n3456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz\n456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{\n56789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|\n6789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}\n789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}\n89:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\n9:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\" <=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%\n=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%& >?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'\n?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'( @ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&' ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'* BCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+ CDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+, DEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,- EFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-. FGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./ GHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0 HIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./01 IJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./012 JKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123 KLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./01234\nLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./012345 MNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456\nNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./01234567 OPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./012345678\nPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789 QRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:\nRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; STUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<\nTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<= UVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>\nVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>? WXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@\nXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@A YZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@AB\nZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABC [\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCD\n\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDE ]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEF\n^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFG _`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGH\n`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHI abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJ\nbcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJK cdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKL\ndefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLM efghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMN\nfghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNO ghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOP\nhijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQ ijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQR\njklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRS klmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRST\nlmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTU mnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUV\nnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVW opqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWX\npqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXY qrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ\nrstuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[ stuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\ntuvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\] uvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^\nvwxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_ wxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`\nxyz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`a yz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`ab\nz{|} !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abc } !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdef\n!\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefg !\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefgh\n\"#$%&'*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghi\n^] telnet> quit\nConnection closed.\nThis continues until the TCP connection is closed as shown in the trace by ending the telnet session.\n\n# Visual Output Simulation\nFor security reasons, most modern machines should have both Telnet and CHARGEN services disabled.\nThe following is a Linux bash script that will simulate the visual appearance of the CHARGEN service in the terminal window.\nThe script can be stopped by pressing Ctrl + C.\n\n# Abuse\nThe service was used maliciously to crash [Microsoft](https://bliptext.com/articles/microsoft) [domain name servers](https://bliptext.com/articles/name-server) (DNS) running [Windows NT 4.0](https://bliptext.com/articles/windows-nt-4-0) by piping the arbitrary characters straight into the DNS server listening port.\nHowever, the attack may have been a symptom of improper buffer management on the part of Microsoft's DNS service and not directly related to the CHARGEN service.\nUDP CHARGEN is commonly used in denial-of-service attacks.\nBy using a fake source address the attacker can send bounce traffic off a UDP CHARGEN application to the victim.\nUDP CHARGEN sends 200 to 1,000 times more data than it receives, depending upon the implementation.\nThis \"traffic multiplication\" is also attractive to an attacker because it obscures the attacker's IP address from the victim.\nCHARGEN was widely implemented on network-connected printers.\nAs printer firmware was rarely updated on older models before CHARGEN and other security concerns were known, there may still be many network-connected printers which implement the protocol.\nWhere these are visible to the Internet, they are invariably misused as denial of service vectors.\nPotential attackers often scan networks looking for UDP port 19 CHARGEN sources.\nSo notorious is the availability of CHARGEN in [printers](https://bliptext.com/articles/printer-computing) that some [distributed denial of service](https://bliptext.com/articles/denial-of-service-attack) trojans now use UDP port 19 for their attack traffic.\nThe supposed aim is to throw investigators off the track; to have them looking for old printers rather than subverted computers.","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T21:44:41.508Z","updated_at":"2025-01-25T21:44:41.508Z","search_vector":"'charact':1 'generat':2 'protocol':3","search_content":" \n \n\n# \nThe **Character Generator Protocol** (**CHARGEN**) is a service of the [Internet Protocol Suite](https://bliptext.com/articles/internet-protocol-suite) defined in in 1983 by [Jon Postel](https://bliptext.com/articles/jon-postel).\nIt is intended for testing, debugging, and measurement purposes.\nThe protocol is rarely used, as its design flaws allow for ready misuse.\nA host may connect to a server that supports the Character Generator Protocol on either [Transmission Control Protocol](https://bliptext.com/articles/transmission-control-protocol) (TCP) or [User Datagram Protocol](https://bliptext.com/articles/user-datagram-protocol) (UDP) [port number](https://bliptext.com/articles/port-number) 19.\nUpon opening a TCP connection, the server starts sending arbitrary characters to the connecting host and continues until the host closes the connection.\nIn the UDP implementation of the protocol, the server sends a UDP datagram containing a random number (between 0 and 512) of characters every time it receives a datagram from the connecting host.\nAny data received by the server is discarded.\n\n# Inetd implementation\nOn most [Unix-like](https://bliptext.com/articles/unix-like) operating systems, a CHARGEN server is built into the [inetd](https://bliptext.com/articles/inetd) or x[inetd](https://bliptext.com/articles/inetd) [daemon](https://bliptext.com/articles/daemon-computer-software).\nThe CHARGEN service is usually not enabled by default.\nIt may be enabled by adding the following lines to the file /etc/inetd.conf and telling inetd to reload its configuration:\nchargen stream tcp nowait root internal\nchargen dgram udp wait root internal\n\n# Applications\nThe CHARGEN service may be used as a source of a byte-stream for debugging TCP network code for proper bounds checking and buffer management.\nIt may also be a source of generic payload for bandwidth measurement and/or QoS fine-tuning.\nConsideration must be given if hardware compression is active, as the output from the CHARGEN service is easily and efficiently compressed.\nThis compression can cause bandwidth tests to report the size of the data after decompression, instead of the actual amount of data which passed the wire.\n\n# Sample session\nA typical CHARGEN service session looks like this: The user connects to the host using a [telnet](https://bliptext.com/articles/telnet) client.\nThe user receives a stream of [bytes](https://bliptext.com/articles/byte).\nAlthough the specific format of the output is not prescribed by, the recommended pattern (and a [de facto standard](https://bliptext.com/articles/de-facto-standard)) is shifted lines of 72 [ASCII](https://bliptext.com/articles/ascii) characters repeating.\n$ telnet localhost chargen\nTrying 127.0.0.1...\nConnected to localhost.\nEscape character is '^]'.\n!\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefg !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefgh\n\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghi $%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijk %&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijkl &'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklm '*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmn *+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmno )*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnop +,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqr ,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrs -./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrst ./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstu /0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuv 0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvw\n123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwx\n23456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxy\n3456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz\n456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{\n56789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|\n6789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}\n789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}\n89:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\n9:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\" ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%\n=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%& >?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'\n?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'( @ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&' ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'* BCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+ CDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+, DEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,- EFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-. FGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./ GHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0 HIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./01 IJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./012 JKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123 KLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./01234\nLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./012345 MNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456\nNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./01234567 OPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./012345678\nPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789 QRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:\nRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; STUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; \nVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ? WXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@\nXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@A YZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@AB\nZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABC [\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCD\n\\]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDE ]^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEF\n^_`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFG _`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGH\n`abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHI abcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJ\nbcdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJK cdefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKL\ndefghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLM efghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMN\nfghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNO ghijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOP\nhijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQ ijklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQR\njklmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRS klmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRST\nlmnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTU mnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUV\nnopqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVW opqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWX\npqrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXY qrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ\nrstuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[ stuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\ntuvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\] uvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^\nvwxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_ wxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`\nxyz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`a yz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`ab\nz{|} !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abc } !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdef\n!\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefg !\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefgh\n\"#$%&'*+,-./0123456789:; ?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghi\n^] telnet> quit\nConnection closed.\nThis continues until the TCP connection is closed as shown in the trace by ending the telnet session.\n\n# Visual Output Simulation\nFor security reasons, most modern machines should have both Telnet and CHARGEN services disabled.\nThe following is a Linux bash script that will simulate the visual appearance of the CHARGEN service in the terminal window.\nThe script can be stopped by pressing Ctrl + C.\n\n# Abuse\nThe service was used maliciously to crash [Microsoft](https://bliptext.com/articles/microsoft) [domain name servers](https://bliptext.com/articles/name-server) (DNS) running [Windows NT 4.0](https://bliptext.com/articles/windows-nt-4-0) by piping the arbitrary characters straight into the DNS server listening port.\nHowever, the attack may have been a symptom of improper buffer management on the part of Microsoft's DNS service and not directly related to the CHARGEN service.\nUDP CHARGEN is commonly used in denial-of-service attacks.\nBy using a fake source address the attacker can send bounce traffic off a UDP CHARGEN application to the victim.\nUDP CHARGEN sends 200 to 1,000 times more data than it receives, depending upon the implementation.\nThis \"traffic multiplication\" is also attractive to an attacker because it obscures the attacker's IP address from the victim.\nCHARGEN was widely implemented on network-connected printers.\nAs printer firmware was rarely updated on older models before CHARGEN and other security concerns were known, there may still be many network-connected printers which implement the protocol.\nWhere these are visible to the Internet, they are invariably misused as denial of service vectors.\nPotential attackers often scan networks looking for UDP port 19 CHARGEN sources.\nSo notorious is the availability of CHARGEN in [printers](https://bliptext.com/articles/printer-computing) that some [distributed denial of service](https://bliptext.com/articles/denial-of-service-attack) trojans now use UDP port 19 for their attack traffic.\nThe supposed aim is to throw investigators off the track; to have them looking for old printers rather than subverted computers.","revisionCount":0},"hasMore":false,"nextCursor":null}

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