ssh-sk-helper.exe stops working in WSL2 if python is installed

[juulSme]

Prerequisites

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Steps to reproduce

I'm using a Yubikey-based FIDO2 ED25519 key (non-discoverable) with WSL2 to connect to an external host with SSH using the ssh-sk_helper.exe as explained in the Yubikey docs (export SSH_SK_HELPER="/mnt/c/Users/me/openssh/ssh-sk-helper.exe"). The WSL2 distro is Debian, the WSL openssh version is OpenSSH_9.2p1 Debian-2+deb12u1, OpenSSL 3.0.11 19 Sep 2023, the Windows openssh version of ssh-sk-helper.exe is the latest OpenSSH_for_Windows_9.4p1, LibreSSL 3.7.3. It works perfectly without having Python installed; I get a Windows prompt asking me to insert the key and touch it. However, when I install Python3, I no longer get the prompt, and the ssh command immediately crashes with obscure output:

me@wsl-debian:~ $ ssh uname@host
Confirm user presence for key ED25519-SK SHA256:PtCgHB6FeWfceiqL8+lSTyUZzVPL21JwlOIs99WmtS8
/mnt/c/Users/me/openssh/ssh-sk-helper.exe: 1: MZ����@��: not found
/mnt/c/Users/me/openssh/ssh-sk-helper.exe: 2: /mnt/c/Users/me/openssh/ssh-sk-helper.exe: 2: $�: not foundEq�m=t��Eq�3:��Eq�3:t�Eq�3:u�4Eq�3:r�.Eq�m=r�.Eq�m=u�6Eq��p��m=p�1Eq�&Ep��Dq��u�Eq��y�iEq�Ŏ�'Eq�&E��'Eq��s�'Eq�Rich&Eq�PEd�p�e�
                                                                                                                                                                                                                                                            %40g@�
                                                                                                                                                                                                                                                                  ��: not found

/mnt/c/Users/me/openssh/ssh-sk-helper.exe: 3: /mnt/c/Users/me/openssh/ssh-sk-helper.exe: 2: Eq�: not found
Syntax error: Unterminated quoted string
/mnt/c/Users/me/openssh/ssh-sk-helper.exe: 2: Eq�: not found
ssh_msg_recv: read header: Connection reset by peer
client_converse: receive: unexpected internal error
reap_helper: helper exited with non-zero exit status
sign_and_send_pubkey: signing failed for ED25519-SK "/home/me/.ssh/id_ed25519_sk_yubikey": unexpected internal error
uname@host: Permission denied (publickey).

I install Python using sudo apt-get install python3 python3-pip python-is-python3 python3-venv. Removing Python with sudo apt-get remove --purge python3 && sudo apt-get autoremove, followed by exiting the virtual machine and wsl --shutdown fixes the issue.

Expected behavior

I expect to be able to install Python without it effecting ssh-sk-helper.exe

Actual behavior

I can't.

Error details

No response

Environment data

PS C:\Users\me> $PsVersionTable

Name                           Value
----                           -----
PSVersion                      7.3.9
PSEdition                      Core
GitCommitId                    7.3.9
OS                             Microsoft Windows 10.0.22621
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

# linux printenv
SHELL=/bin/bash
WSL2_GUI_APPS_ENABLED=1
WSL_DISTRO_NAME=Debian
WT_SESSION=a8060c0a-4e9f-4fb8-90f0-12be332e6e27
SSH_SK_HELPER=/mnt/c/Users/me/openssh/ssh-sk-helper.exe
SSH_AUTH_SOCK=/home/me/.ssh/ssh-agent.sock
NAME=wsl-debian
PWD=/home/me
LOGNAME=me
HOME=/home/me
LANG=en_US.UTF-8
WSL_INTEROP=/run/WSL/301_interop
LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=00:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.wim=01;31:*.swm=01;31:*.dwm=01;31:*.esd=01;31:*.avif=01;35:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.webp=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:*~=00;90:*#=00;90:*.bak=00;90:*.old=00;90:*.orig=00;90:*.part=00;90:*.rej=00;90:*.swp=00;90:*.tmp=00;90:*.dpkg-dist=00;90:*.dpkg-old=00;90:*.ucf-dist=00;90:*.ucf-new=00;90:*.ucf-old=00;90:*.rpmnew=00;90:*.rpmorig=00;90:*.rpmsave=00;90:
WAYLAND_DISPLAY=wayland-0
LESSCLOSE=/usr/bin/lesspipe %s %s
TERM=xterm-256color
LESSOPEN=| /usr/bin/lesspipe %s
USER=me
DISPLAY=:0
SHLVL=1
XDG_RUNTIME_DIR=/run/user/1000/
WSLENV=WT_SESSION:WT_PROFILE_ID:
KUBE_EDITOR=nano
PATH=/home/me/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/wsl/lib:/mnt/c/Users/me/bin:/mnt/c/Program Files/WindowsApps/Microsoft.PowerShell_7.3.9.0_x64__8wekyb3d8bbwe:/mnt/c/Windows/system32:/mnt/c/Windows:/mnt/c/Windows/System32/Wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0/:/mnt/c/Windows/System32/OpenSSH/:/mnt/c/Program Files/Yubico/Yubico PIV Tool/bin:/mnt/c/Program Files/PuTTY/:/mnt/c/Users/me/bin:/mnt/c/Users/me/go/bin:/mnt/c/Users/me/openssh:/mnt/c/Users/me/AppData/Local/Microsoft/WindowsApps:/mnt/c/Users/me/AppData/Local/Programs/Microsoft VS Code/bin:/mnt/c/Users/me/AppData/Local/Programs/Git/cmd:~/projects/linux_config/bin:~/bin
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
HOSTTYPE=x86_64
PULSE_SERVER=unix:/mnt/wslg/PulseServer
WT_PROFILE_ID={574e775e-4f2a-5b96-ac1e-a2962a402336}
_=/usr/bin/printenv

Version

9,4

Visuals

No response

[maertendMSFT]

does this persist on a SSH session outside of WSL? The installed SSH in WSL is not Win32-OpenSSH, thus is considered out of scope for this repo.

[tfriedel]

This fixed it for me:

1. Create binformat config file

microsoft/WSL#8986 (comment)

in wsl create the file

sudo vim /usr/lib/binfmt.d/WSLInterop.conf 

with contents:

:WSLInterop:M::MZ::/init:PF

2. restart binformat related systemd services

microsoft/WSL#8986 (comment)

restart systemd services

sudo systemctl restart systemd-binfmt
sudo systemctl restart binfmt-support

3. install binformat systemd support

If you get an error on restarting, you might need to install binformat support first:

sudo apt update
sudo apt install binfmt-support

4. check config

if you see

sudo ls -Fal /proc/sys/fs/binfmt_misc
total 0
drwxr-xr-x 2 root root 0 Mar 24 11:11 ./
dr-xr-xr-x 1 root root 0 Mar 24 11:11 ../
-rw-r--r-- 1 root root 0 Mar 24 11:35 WSLInterop
-rw-r--r-- 1 root root 0 Mar 24 11:35 jar
-rw-r--r-- 1 root root 0 Mar 24 11:35 python3.11
--w------- 1 root root 0 Mar 24 11:35 register
-rw-r--r-- 1 root root 0 Mar 24 11:35 status

sudo cat /proc/sys/fs/binfmt_misc/WSLInterop
enabled
interpreter /init
flags: PF
offset 0
magic 4d5a

everything should work fine also with systemd again.

from: https://www.reddit.com/r/bashonubuntuonwindows/comments/11vx61n/wsl2_error_cannot_execute_binary_file_exec_format/jdh2ovy/

[juulSme]

Wonderful, thank you :)