ConnectBot crashes when connecting to SSH servers

Bug description

ConnectBot crashes when trying to connect to any of several SSH severs. This happens using password or public-key (tested with RSA) authentication.

Steps to reproduce

1. Open ConnectBot
2. Touch a host to start an SSH connection
3. Crash

Expected behavior

Should see a remote shell prompt instead of crash.

Android device

• OS: Android 7.0
• ConnectBot Version: 1.9.7 (beta from Play Store)

Server information

(one of them:)

• OS: Ubuntu Server 20.04 LTS
• SSH Software and Version: OpenSSH_8.2p1 Ubuntu-4ubuntu0.1, OpenSSL 1.1.1f 31 Mar 2020
• Pubkeys used (if applicable): Ed25519

Additional context

Everything worked fine before the last ConnectBot update; although I’m not sure which version was installed, it was up-to date with whichever version was available before on the Play Store (beta enabled).

Here’s the server log and stacktrace (from ADB) for the same connection:

• server.log

Jul 11 23:13:05 ubuntu sshd[3520]: message repeated 8 times: [ debug1: server_input_global_request: rtype [e-mail] want_reply 1]
Jul 11 23:13:06 ubuntu sshd[3419]: debug1: Forked child 3530.
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: Set /proc/self/oom_score_adj to 0
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: rexec start in 5 out 5 newsock 5 pipe 7 sock 8
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: inetd sockets after dupping: 4, 4
Jul 11 23:13:06 ubuntu sshd[3530]: Connection from 10.0.1.11 port 42893 on 10.0.0.123 port 22 rdomain ""
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.1
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: Remote protocol version 2.0, remote software version TrileadSSH2Java_213
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: no match: TrileadSSH2Java_213
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: permanently_set_uid: 111/65534 [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: list_hostkey_types: rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256,ssh-ed25519 [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: SSH2_MSG_KEXINIT sent [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: SSH2_MSG_KEXINIT received [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: kex: algorithm: curve25519-sha256 [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: kex: host key algorithm: ssh-ed25519 [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: kex: client->server cipher: aes256-ctr MAC: [e-mail] compression: none [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: kex: server->client cipher: aes256-ctr MAC: [e-mail] compression: none [preauth]
Jul 11 23:13:06 ubuntu sshd[3530]: debug1: expecting SSH2_MSG_KEX_ECDH_INIT [preauth]

• stacktrace.txt

07-12 00:13:06.185 15275 15321 E AndroidRuntime: FATAL EXCEPTION: Thread-4
07-12 00:13:06.185 15275 15321 E AndroidRuntime: Process: org.connectbot, PID: 15275
07-12 00:13:06.185 15275 15321 E AndroidRuntime: java.lang.IllegalStateException: Arithmetic error in curve multiplication with the public key: 0900000000000000000000000000000000000000000000000000000000000000
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.google.crypto.tink.subtle.Curve25519.curveMult(Curve25519.java:332)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.google.crypto.tink.subtle.X25519.computeSharedSecret(X25519.java:103)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.google.crypto.tink.subtle.X25519.publicFromPrivate(X25519.java:121)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.trilead.ssh2.crypto.dh.Curve25519Exchange.init(Curve25519Exchange.java:43)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:574)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:614)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:310)
07-12 00:13:06.185 15275 15321 E AndroidRuntime: 	at java.lang.Thread.run(Thread.java:761)

Regarding the “public key” seen on the stacktrace (0900000000000000000000000000000000000000000000000000000000000000): I’ve seen stacktraces with different, maybe random, values there before. But now every host I test crashes with that value there, everytime.

[thaidn]

Thanks @kruton.

Just an update: I’ve bought an ASUS phone running MediaTek and will have it in a week. Will update once I’ve got more information.

[luismrsilva]

I’ve managed to reproduce the crash with the debug variant of ConnectBot using the debugImplementation of sshlib 2.2.14 and tink 1.4.0-rc2. I set a breakpoint on the line where the IllegalStateException is thrown to read the variables from memory for 3 separate instances of the crash. These include the variables for each scope leading to the private key. Here are the privateKey values and other variables:

• privateKey = {119, 127, 11, -105, -122, -51, -112, 119, -27, 112, -79, 72, -59, 105, 100, 111, 119, -18, 81, -76, 104, -81, 55, 8, 42, -77, -1, 39, 64, 124, 83, -69}; from variables_crash1.txt

• privateKey = {-73, 17, 51, 40, 0, 92, 31, 85, -16, 53, 86, 8, -64, 99, 63, -72, 38, -123, 37, -25, -54, -97, -126, 104, 11, -94, -56, -119, 14, -45, 62, -111}; from variables_crash2.txt

• privateKey = {127, -83, -16, 85, -38, 15, 97, -44, -19, 80, 109, 68, 2, 100, 103, -71, -41, 87, 115, 10, -27, -58, -86, -39, -52, 31, -1, 32, -72, 46, 86, -115}; from variables_crash3.txt

Please let me know if you need more info or if there is a better way to present these.