[ANNOUNCEMENT] Updated: OpenSSH-7.5p1-1

[Lionel Fourquaux]

> * This release deprecates the sshd_config UsePrivilegeSeparation
>   option, thereby making privilege separation mandatory.

This has (probably not wholly intended) consequences when running sshd in 
single user (non root) mode:

$ /usr/sbin/sshd -D -f ~/.ssh/sshd_config
Privilege separation user sshd does not exist

The problem is not limited to Cygwin, but is unlikely to happen in 
a typical Unix, since ssh is probably installed globally.

If Cygwin was installed without administrative privileges, creating 
a dedicated sshd user would be impossible (and makes little sense if sshd 
runs in single user mode, anyway).  I guess it would be possible to add 
a fake user account in /etc/passwd.

Since user sshd and chroot /var/empty are not used in single user mode, 
it might be better to remove the check in this case:

=== cut after ===
diff --git a/sshd.c b/sshd.c
index 010a2c3..4f9b2c8 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1641,7 +1641,8 @@ main(int ac, char **av)
 
 	/* Store privilege separation user for later use if required. */
 	if ((privsep_pw = getpwnam(SSH_PRIVSEP_USER)) == NULL) {
-		if (use_privsep || options.kerberos_authentication)
+		if ((use_privsep || options.kerberos_authentication)
+		    && (getuid() == 0 || geteuid() == 0))
 			fatal("Privilege separation user %s does not exist",
 			    SSH_PRIVSEP_USER);
 	} else {
@@ -1767,7 +1768,7 @@ main(int ac, char **av)
 		    key_type(key));
 	}
 
-	if (use_privsep) {
+	if (use_privsep && (getuid() == 0 || geteuid() == 0)) {
 		struct stat st;
 
 		if ((stat(_PATH_PRIVSEP_CHROOT_DIR, &st) == -1) ||
=== cut before ===

Best regards,

		-- Lionel

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