** Also affects: openssh (Ubuntu Hirsute)
Importance: Undecided
Status: New
** Also affects: openssh (Ubuntu Focal)
Importance: Undecided
Status: New
** Changed in: openssh (Ubuntu Focal)
Status: New => Triaged
** Changed in: openssh (Ubuntu Hirsute)
Status: New => Triaged
** Tags added: server-next
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https://bugs.launchpad.net/bugs/1938144
Title:
monitor_read: unpermitted request 48 on server while attempting GSSAPI
key exchange
Status in portable OpenSSH:
Unknown
Status in openssh package in Ubuntu:
Triaged
Status in openssh source package in Focal:
Triaged
Status in openssh source package in Hirsute:
Triaged
Bug description:
I'm using openssh 1:8.2p1-4ubuntu0.2 on Ubuntu 20.04.2 LTS (client and
server) with the option "GSSAPIKeyExchange=yes", and this causes the
connection to fail. The server has GSSAPI (Kerberos authentication)
enabled, but is is only used for non-root users (root uses SSH keys).
Client command:
ssh -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex
root@server -v -p 2222 -o GSSAPIKeyExchange=yes
Client log:
OpenSSH_8.2p1 Ubuntu-4ubuntu0.2, OpenSSL 1.1.1f 31 Mar 2020
debug1: Reading configuration data /home/user/.ssh/config
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 *
debug1: Connecting to compute-test [130.75.80.46] port 2222.
debug1: Connection established.
debug1: identity file /home/rother/.ssh/id_rsa type 0
debug1: identity file /home/rother/.ssh/id_rsa-cert type -1
debug1: identity file /home/rother/.ssh/id_dsa type -1
debug1: identity file /home/rother/.ssh/id_dsa-cert type -1
debug1: identity file /home/rother/.ssh/id_ecdsa type -1
debug1: identity file /home/rother/.ssh/id_ecdsa-cert type -1
debug1: identity file /home/rother/.ssh/id_ecdsa_sk type -1
debug1: identity file /home/rother/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /home/rother/.ssh/id_ed25519 type -1
debug1: identity file /home/rother/.ssh/id_ed25519-cert type -1
debug1: identity file /home/rother/.ssh/id_ed25519_sk type -1
debug1: identity file /home/rother/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /home/rother/.ssh/id_xmss type -1
debug1: identity file /home/rother/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.2p1
Ubuntu-4ubuntu0.2
debug1: match: OpenSSH_8.2p1 Ubuntu-4ubuntu0.2 pat OpenSSH* compat 0x04000000
debug1: Authenticating to server:2222 as 'root'
debug1: Offering GSSAPI proposal:
gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-gex-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group14-sha1-eipGX3TCiQSrx573bT1o1Q==
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1...@openssh.com MAC:
<implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1...@openssh.com MAC:
<implicit> compression: none
debug1: Doing group exchange
debug1: Calling gss_init_sec_context
debug1: Delegating credentials
debug1: Received GSSAPI_COMPLETE
debug1: Calling gss_init_sec_context
debug1: Delegating credentials
debug1: Rekey has happened - updating saved versions
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: /home/rother/.ssh/id_rsa RSA
SHA256:n/EY/cGjgd/r+7JpuqODxIotHHLsYptGXYx9GlKCWSM agent
debug1: Will attempt key: /home/rother/.ssh/root_id_rsa RSA
SHA256:yCLAID9FMILharHmDpCB8wW8eiA+iHa4oQKLODbbzKw agent
debug1: Will attempt key: /home/user/.ssh/id_dsa
debug1: Will attempt key: /home/user/.ssh/id_ecdsa
debug1: Will attempt key: /home/user/.ssh/id_ecdsa_sk
debug1: Will attempt key: /home/user/.ssh/id_ed25519
debug1: Will attempt key: /home/user/.ssh/id_ed25519_sk
debug1: Will attempt key: /home/user/.ssh/id_xmss
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info:
server-sig-algs=<ssh-ed25519,sk-ssh-ed25...@openssh.com,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp...@openssh.com>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-with-mic
debug1: Delegating credentials
debug1: Delegating credentials
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
Connection closed by 1.2.3.4 port 2222
Server log:
debug1: sshd version OpenSSH_8.2, OpenSSL 1.1.1f 31 Mar 2020
debug1: private host key #0: ssh-rsa SHA256:REDACTED
debug1: private host key #1: ecdsa-sha2-nistp256 SHA256:REDACTED
debug1: private host key #2: ssh-ed25519 SHA256:REDACTED
debug1: rexec_argv[0]='/usr/sbin/sshd'
debug1: rexec_argv[1]='-d'
debug1: rexec_argv[2]='-p'
debug1: rexec_argv[3]='2222'
debug1: Set /proc/self/oom_score_adj from 0 to -1000
debug1: Bind to port 2222 on 0.0.0.0.
Server listening on 0.0.0.0 port 2222.
debug1: Bind to port 2222 on ::.
Server listening on :: port 2222.
debug1: Server will not fork when running in debugging mode.
debug1: rexec start in 5 out 5 newsock 5 pipe -1 sock 8
debug1: sshd version OpenSSH_8.2, OpenSSL 1.1.1f 31 Mar 2020
debug1: private host key #0: ssh-rsa SHA256:REDACTED
debug1: private host key #1: ecdsa-sha2-nistp256 SHA256:REDACTED
debug1: private host key #2: ssh-ed25519 SHA256:REDACTED
debug1: inetd sockets after dupping: 3, 3
Connection from 1.2.3.5 port 53724 on 1.2.3.4 port 2222 rdomain ""
debug1: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.2p1
Ubuntu-4ubuntu0.2
debug1: match: OpenSSH_8.2p1 Ubuntu-4ubuntu0.2 pat OpenSSH* compat 0x04000000
debug1: permanently_set_uid: 111/65534 [preauth]
debug1: list_hostkey_types:
rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256,ssh-ed25519 [preauth]
debug1: SSH2_MSG_KEXINIT sent [preauth]
debug1: SSH2_MSG_KEXINIT received [preauth]
debug1: kex: algorithm: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g== [preauth]
debug1: kex: host key algorithm: ecdsa-sha2-nistp256 [preauth]
debug1: kex: client->server cipher: chacha20-poly1...@openssh.com MAC:
<implicit> compression: none [preauth]
debug1: kex: server->client cipher: chacha20-poly1...@openssh.com MAC:
<implicit> compression: none [preauth]
debug1: Doing group exchange [preauth]
debug1: Wait SSH2_MSG_GSSAPI_INIT [preauth]
debug1: Received some client credentials
debug1: rekey out after 134217728 blocks [preauth]
debug1: SSH2_MSG_NEWKEYS sent [preauth]
debug1: Sending SSH2_MSG_EXT_INFO [preauth]
debug1: expecting SSH2_MSG_NEWKEYS [preauth]
debug1: SSH2_MSG_NEWKEYS received [preauth]
debug1: rekey in after 134217728 blocks [preauth]
debug1: KEX done [preauth]
debug1: userauth-request for user root service ssh-connection method none
[preauth]
debug1: attempt 0 failures 0 [preauth]
debug1: PAM: initializing for "root"
debug1: PAM: setting PAM_RHOST to "1.2.3.5"
debug1: PAM: setting PAM_TTY to "ssh"
debug1: userauth-request for user root service ssh-connection method
gssapi-with-mic [preauth]
debug1: attempt 1 failures 0 [preauth]
Postponed gssapi-with-mic for root from 1.2.3.5 port 53724 ssh2 [preauth]
debug1: Received some client credentials
Failed gssapi-with-mic for root from 1.2.3.5 port 53724 ssh2
debug1: userauth-request for user root service ssh-connection method
gssapi-with-mic [preauth]
debug1: attempt 2 failures 1 [preauth]
debug1: userauth-request for user root service ssh-connection method
gssapi-keyex [preauth]
debug1: attempt 3 failures 1 [preauth]
monitor_read: unpermitted request 48
debug1: do_cleanup
debug1: PAM: cleanup
debug1: Killing privsep child 5525
debug1: audit_event: unhandled event 12
The important line might be "monitor_read: unpermitted request 48"
When disabling GSSAPIKeyExchange=yes, everything works as expected.
This bug was discovered using Ansible, which uses "-o
PreferredAuthentications=gssapi-with-mic,gssapi-
keyex,hostbased,publickey" for it's ssh connections.
A similar bugs was reported in RHEL 7:
https://bugzilla.redhat.com/show_bug.cgi?id=1162620
Please let me know if you need any further information!
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