ui_login_bugs » Revisions »

Differences

This shows you the differences between the selected revisions of the page.

2017-01-18		2017-01-18
explicit anchors + standardizing anchor (martin)		explicit anchor use (martin)
	Line 87:		Line 87:
	An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol which can be sent from the client to the server, or from the server to the client, at any time. Either side is required to ignore the message whenever it receives it. WinSCP uses ignore messages to hide the password packet in SSH-1, so that a listener cannot tell the length of the user's password; it also uses ignore messages for [[ui_login_connection#keepalives\|connection keepalives]].		An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol which can be sent from the client to the server, or from the server to the client, at any time. Either side is required to ignore the message whenever it receives it. WinSCP uses ignore messages to hide the password packet in SSH-1, so that a listener cannot tell the length of the user's password; it also uses ignore messages for [[ui_login_connection#keepalives\|connection keepalives]].

-	If this bug is detected, WinSCP will stop using ignore messages. This means that keepalives will stop working, and WinSCP will have to fall back to a secondary defense against [[#refuses_all_ssh-1_password_camouflage\|SSH-1 password-length eavesdropping]]. If this bug is enabled when talking to a correct server, the session will succeed, but keepalives will not work and the session might be more vulnerable to eavesdroppers than it could be.	+	If this bug is detected, WinSCP will stop using ignore messages. This means that keepalives will stop working, and WinSCP will have to fall back to a secondary defense against [[#sshbug_plainpw1\|SSH-1 password-length eavesdropping]]. If this bug is enabled when talking to a correct server, the session will succeed, but keepalives will not work and the session might be more vulnerable to eavesdroppers than it could be.

	This is an %%SSH-1%%-specific bug. No known %%SSH-2%% server fails to deal with %%SSH-2%% ignore messages.		This is an %%SSH-1%%-specific bug. No known %%SSH-2%% server fails to deal with %%SSH-2%% ignore messages.

	===== [[sshbug_plainpw1]] Refuses all SSH-1 password camouflage =====		===== [[sshbug_plainpw1]] Refuses all SSH-1 password camouflage =====
-	When talking to an SSH-1 server which cannot deal with [[#chokes_on_ssh-1_ignore_messages\|ignore messages]], WinSCP will attempt to disguise the length of the user's password by sending additional padding within the password packet. This is technically a violation of the %%SSH-1%% specification, and so WinSCP will only do it when it cannot use standards-compliant ignore messages as camouflage. In this sense, for a server to refuse to accept a padded password packet is not really a bug, but it does make life inconvenient if the server can also not handle ignore messages.	+	When talking to an SSH-1 server which cannot deal with [[#sshbug_ignore1\|ignore messages]], WinSCP will attempt to disguise the length of the user's password by sending additional padding within the password packet. This is technically a violation of the %%SSH-1%% specification, and so WinSCP will only do it when it cannot use standards-compliant ignore messages as camouflage. In this sense, for a server to refuse to accept a padded password packet is not really a bug, but it does make life inconvenient if the server can also not handle ignore messages.

	If this bug is detected, WinSCP will assume that neither ignore messages nor padding are acceptable, and that it thus has no choice but to send the user's password with no form of camouflage, so that an eavesdropping user will be easily able to find out the exact length of the password. If this bug is enabled when talking to a correct server, the session will succeed, but will be more vulnerable to eavesdroppers than it could be.		If this bug is detected, WinSCP will assume that neither ignore messages nor padding are acceptable, and that it thus has no choice but to send the user's password with no form of camouflage, so that an eavesdropping user will be easily able to find out the exact length of the password. If this bug is enabled when talking to a correct server, the session will succeed, but will be more vulnerable to eavesdroppers than it could be.