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Zabezpieczenie serwera OpenSSH - ciekawostki...

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Zabezpieczenie serwera OpenSSH - ciekawostki...

: 25 maja 2011, 15:20
autor: adasiek_j
Ten artykuł powstał dla tych wszystkich, którzy boją się, że ich serwer jest narażony bardziej na ataki niż inne serwery.

Witam.
Ostatnio przeskanowałem sobie Debiana nmapem i w wynikach otrzymałem między innymi coś takiego:

Kod: Zaznacz cały

7532/tcp open  ssh     OpenSSH 5.1p1 Debian 5 (protocol 2.0)
| ssh-hostkey: 1024 58:30:41:09:93:cd:a0:54:a4:xx:xx:xx:xx:xx:xx:xx (DSA)
|_2048 34:d0:f1:02:99:17:1b:47:51:xx:xx:xx:xx:xx:xx:xx (RSA)
  1. Zastanawiam się, czy przypadkiem mój Debian nie chwali się zbyt dużą ilością informacji?
  2. Dodatkowo mam pytanie czy te informację mogą w jakiś sposób ułatwić robotę potencjalnemu hakerowi?
  3. No i na koniec jak ograniczyć/wyłączyć wyświetlanie tych informacji? Jak się zabezpieczyć?
Tutaj poniżej pokażę Ci prosty przykład, jak może wyglądać połączenie ssh do serwera:
  1. Połączenie podstawowe, jakie wiele osób wykonuje:

    Kod: Zaznacz cały

    adasiek@sea-star:~$ ssh -l root -C 192.168.6.254

    Kod: Zaznacz cały

    Last login: Fri May 20 09:04:17 2011 from 192.168.6.164
Have a lot of fun...
serek-hurt:~ #
  2. Teraz drobna zmiana polecenia:

    Kod: Zaznacz cały

    adasiek@sea-star:~$ ssh -l root -C 192.168.6.254 -v

    Kod: Zaznacz cały

    OpenSSH_5.5p1 Debian-4ubuntu5, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /home/adasiek/.ssh/config
debug1: Applying options for *
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.6.254 [192.168.6.254] port 22.
debug1: Connection established.
debug1: identity file /home/adasiek/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-1024
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-1024
debug1: identity file /home/adasiek/.ssh/id_rsa-cert type -1
debug1: identity file /home/adasiek/.ssh/id_dsa type -1
debug1: identity file /home/adasiek/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 1.99, remote software version OpenSSH_4.1
debug1: match: OpenSSH_4.1 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-4ubuntu5
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 zlib
debug1: kex: client->server aes128-ctr hmac-md5 zlib
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host '192.168.6.254' is known and matches the RSA host key.
debug1: Found key in /home/adasiek/.ssh/known_hosts:75
debug1: ssh_rsa_verify: signature correct
debug1: Enabling compression at level 6.
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Offering public key: /home/adasiek/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 149
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = pl_PL.utf8
Last login: Fri May 20 09:04:26 2011 from 192.168.6.164
Have a lot of fun...
serek-hurt:~ # 

serek-hurt:~ # logout
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
Connection to 192.168.6.254 closed.
Transferred: sent 1912, received 1960 bytes, in 61.9 seconds
Bytes per second: sent 30.9, received 31.7
debug1: Exit status 1
debug1: compress outgoing: raw data 1067, compressed 659, factor 0.62
debug1: compress incoming: raw data 492, compressed 421, factor 0.86
adasiek@sea-star:~$
  3. I jeszcze kolejna modyfikacja polecenia:

    Kod: Zaznacz cały

    adasiek@sea-star:~$ ssh -l root -C 192.168.6.254 -vv

    Kod: Zaznacz cały

    OpenSSH_5.5p1 Debian-4ubuntu5, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /home/adasiek/.ssh/config
debug1: Applying options for *
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to 192.168.6.254 [192.168.6.254] port 22.
debug1: Connection established.
debug2: key_type_from_name: unknown key type '-----BEGIN'
debug2: key_type_from_name: unknown key type '-----END'
debug1: identity file /home/adasiek/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-1024
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-1024
debug1: identity file /home/adasiek/.ssh/id_rsa-cert type -1
debug1: identity file /home/adasiek/.ssh/id_dsa type -1
debug1: identity file /home/adasiek/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 1.99, remote software version OpenSSH_4.1
debug1: match: OpenSSH_4.1 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-4ubuntu5
debug2: fd 3 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: [email protected],[email protected],ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: [email protected],zlib,none
debug2: kex_parse_kexinit: [email protected],zlib,none
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-ctr hmac-md5 zlib
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-ctr hmac-md5 zlib
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug2: dh_gen_key: priv key bits set: 123/256
debug2: bits set: 504/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host '192.168.6.254' is known and matches the RSA host key.
debug1: Found key in /home/adasiek/.ssh/known_hosts:75
debug2: bits set: 540/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: Enabling compression at level 6.
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/adasiek/.ssh/id_rsa (0x7f2eed3ad0f0)
debug2: key: /home/adasiek/.ssh/id_dsa ((nil))
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Offering public key: /home/adasiek/.ssh/id_rsa
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-rsa blen 149
debug2: input_userauth_pk_ok: fp 07:f1:73:35:27:b4:3e:c4:a8:cb:f1:9b:bc:f5:10:a1
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug2: channel 0: send open
debug1: Entering interactive session.
debug2: callback start
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug1: Sending environment.
debug1: Sending env LANG = pl_PL.utf8
debug2: channel 0: request env confirm 0
debug2: channel 0: request shell confirm 1
debug2: fd 3 setting TCP_NODELAY
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 131072
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
Last login: Fri May 20 09:06:10 2011 from 192.168.6.164
Have a lot of fun...
serek-hurt:~ # logout
debug2: channel 0: rcvd eof
debug2: channel 0: output open -> drain
debug2: channel 0: obuf empty
debug2: channel 0: close_write
debug2: channel 0: output drain -> closed
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug2: channel 0: rcvd close
debug2: channel 0: close_read
debug2: channel 0: input open -> closed
debug2: channel 0: almost dead
debug2: channel 0: gc: notify user
debug2: channel 0: gc: user detached
debug2: channel 0: send close
debug2: channel 0: is dead
debug2: channel 0: garbage collecting
debug1: channel 0: free: client-session, nchannels 1
Connection to 192.168.6.254 closed.
Transferred: sent 1848, received 1848 bytes, in 1.7 seconds
Bytes per second: sent 1095.0, received 1095.0
debug1: Exit status 0
debug1: compress outgoing: raw data 1033, compressed 640, factor 0.62
debug1: compress incoming: raw data 420, compressed 388, factor 0.92
adasiek@sea-star:~$
Teraz pomyśl, te wszystkie informacje to tylko część tego, co w ogóle komputery wymieniają pomiędzy sobą. Jeśli chcesz, możesz odłączyć zasilanie serwera, ale jeśli chcesz, aby działał, to po prostu utrzymuj aktualne wersje oprogramowania, ewentualnie polecam pakiety w stylu http://www.fail2ban.org/wiki/index.php/Main_Page

Pozdrawiam,
Adam

: 25 maja 2011, 16:39
autor: Yampress
to jeszcze sobie zrób -vvv i wklej bo przeklejać umiesz :) temat nie wnosi niczego . powinien być skasowany.
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