curl fails to do password authentication with sftp using libssh backend

[And-yW]

I did this

I get this:
curl -v -s -S --connect-timeout 10 --hostpubsha256 "HASH" -u "user:pass" -T /tmp/slask.bin -g sftp://192.168.0.20
2/tmp/

• SSH: private key file ''
• Trying 192.168.0.202:22...
• Established connection to 192.168.0.202 (192.168.0.202 port 22) from 192.168.0.207 port 47726
• User: user
• SSH SHA256 fingerprint:
• SSH authentication methods available: public key, keyboard-interactive, password
• Authentication using SSH public key file
• Could not load private key file
• closing connection #0
  curl: (67) Could not load private key file

I've attached a patch that solves the issue, the problem seems to be that libssh.c only NULL checks sshc->priv_key but its set to "".

0001-libssh-Handle-empty-private-key.patch

I expected the following

That it works.

curl/libcurl version

curl 8.22.0 (aarch64-poky-linux-gnu) libcurl/8.22.0 OpenSSL/3.5.7 zlib/1.3.2 libssh/0.11.5/openssl/zlib
Release-Date: 2026-09-02
Protocols: dict file ftp ftps http https imap imaps ipfs ipns pop3 pop3s rtsp scp sftp smtp smtps tftp ws wss
Features: alt-svc HSTS HTTPS-proxy IPv6 Largefile libz SSL threadsafe UnixSockets

operating system

Linux 5.15.167-rel-5.15-artpec8-951 #1 SMP PREEMPT Thu Sep 10 16:06:46 UTC 2026 aarch64 GNU/Linux

[bagder]

@And-yW are you up to creating a PR based on that or should I do it for you?

[icing]

Done in #23082

[And-yW]

Great, thanks