TryHackMeでSSH接続したいのに、なかなかできずに苦戦したので、備忘録として残しておきます。
同じように悩んでいる方がいれば、参考にしてもらえるといいかなと思います。
おすすめの参考書
ポチップ
著:Justin Seitz, 著:Tim Arnold, 監修:萬谷 暢崇, 翻訳:新井 悠, 翻訳:加唐 寛征, 翻訳:村上 涼
¥3,520 （2024/07/21 08:07時点 | Amazon調べ）
ポチップ
著:徳丸 浩
¥3,168 （2024/07/25 10:21時点 | Amazon調べ）
ポチップ
目次
expecting SSH2_MSG_KEX_DH_GEX_GROUPで処理が止まっている場合
事象を確認するために、「-vvv」をつけてsshしてみました。
┌──(hacklab㉿hacklab)-[~]
└─$ ssh user@10.10.237.121 -vvv 130 ⨯
OpenSSH_8.7p1 Debian-4, OpenSSL 1.1.1m 14 Dec 2021
debug1: Reading configuration data /home/hacklab/.ssh/config
debug1: /home/hacklab/.ssh/config line 1: Applying options for *
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug2: resolve_canonicalize: hostname 10.10.237.121 is address
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/home/hacklab/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/home/hacklab/.ssh/known_hosts2'
debug3: ssh_connect_direct: entering
debug1: Connecting to 10.10.237.121 [10.10.237.121] port 22.
debug3: set_sock_tos: set socket 3 IP_TOS 0x10
debug1: Connection established.
debug1: identity file /home/hacklab/.ssh/id_rsa type -1
debug1: identity file /home/hacklab/.ssh/id_rsa-cert type -1
debug1: identity file /home/hacklab/.ssh/id_dsa type -1
debug1: identity file /home/hacklab/.ssh/id_dsa-cert type -1
debug1: identity file /home/hacklab/.ssh/id_ecdsa type -1
debug1: identity file /home/hacklab/.ssh/id_ecdsa-cert type -1
debug1: identity file /home/hacklab/.ssh/id_ecdsa_sk type -1
debug1: identity file /home/hacklab/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /home/hacklab/.ssh/id_ed25519 type -1
debug1: identity file /home/hacklab/.ssh/id_ed25519-cert type -1
debug1: identity file /home/hacklab/.ssh/id_ed25519_sk type -1
debug1: identity file /home/hacklab/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /home/hacklab/.ssh/id_xmss type -1
debug1: identity file /home/hacklab/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.7p1 Debian-4
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-6+squeeze5
debug1: compat_banner: match: OpenSSH_5.5p1 Debian-6+squeeze5 pat OpenSSH_5* compat 0x0c000002
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to 10.10.237.121:22 as 'user'
debug1: load_hostkeys: fopen /home/hacklab/.ssh/known_hosts: No such file or directory
debug1: load_hostkeys: fopen /home/hacklab/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug3: order_hostkeyalgs: no algorithms matched; accept original
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c
debug2: host key algorithms: ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: host key algorithms: ssh-rsa,ssh-dss
debug2: ciphers ctos: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: ciphers stoc: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: MACs ctos: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: MACs stoc: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug1: kex: algorithm: diffie-hellman-group-exchange-sha256
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: aes128-ctr MAC: umac-64@openssh.com compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: umac-64@openssh.com compression: none
debug3: send packet: type 34
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(2048<3072<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
Connection closed by 10.10.237.121 port 22確認すると「expecting SSH2_MSG_KEX_DH_GEX_GROUP」で止まっているのがわかりました。。。
少し調べていると、MTU値が悪さをしているという記事をいくつか見つけたので。
まずは、MTU値を確認しておくと、eth0は1500となっていることがわかりました。
┌──(hacklab㉿hacklab)-[~]
└─$ ifconfig 127 ⨯
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
...とりあえず、eth0を1454にしておきます。
┌──(hacklab㉿hacklab)-[~]
└─$ sudo ifconfig eth0 mtu 1454 この状態でもう一度sshをしてみると、うまくいきました！！
┌──(hacklab㉿hacklab)-[~]
└─$ ssh user@10.10.237.121
user@10.10.237.121's password:
Linux debian 2.6.32-5-amd64 #1 SMP Tue May 13 16:34:35 UTC 2014 x86_64
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Wed Apr 5 11:11:52 2023 from ip-10-18-110-90.eu-west-1.compute.internal
user@debian:~$まとめ
サーバーは起動しているのに、「Connection closed」で焦りましたが、なんとか接続できたのでよかったです。
参考文献・サイト
@IT：https://atmarkit.itmedia.co.jp/flinux/rensai/linuxtips/418chkmtu.html
