Sergey Panov created SSHD-1229:
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Summary: Infinite clientMethods iteration in ClientUserAuthService
Key: SSHD-1229
URL: https://issues.apache.org/jira/browse/SSHD-1229
Project: MINA SSHD
Issue Type: Bug
Affects Versions: 2.7.0
Reporter: Sergey Panov
Hello,
I've come across that the
org.apache.sshd.client.session.ClientUserAuthService#clientMethods list could
be iterated over and over again until a client terminates connection. This
happens when a server requires two-factor authentication. Despite RFC 4252
([https://www.ietf.org/rfc/rfc4252.txt)] recommends the server returning only
authentication methods that have not been successfully completed, some
implementations ignore this. If the authentication is partially successful, but
the server returns the same list of authentication methods, the 0th client
authentication method will be used repeatedly.
{code:java}
protected void processUserAuth(Buffer buffer) throws Exception {
...
if (cmd == SshConstants.SSH_MSG_USERAUTH_FAILURE) {
String mths = buffer.getString();
boolean partial = buffer.getBoolean();
if (log.isDebugEnabled()) {
log.debug("processUserAuth({}) Received
SSH_MSG_USERAUTH_FAILURE - partial={}, methods={}",
session, partial, mths);
}
if (partial || (serverMethods == null)) {
serverMethods = Arrays.asList(GenericUtils.split(mths, ','));
// If a server is always returning the same list of methods, the "next" client
method in clientMethods will be on index 0
currentMethod = 0;
if (userAuth != null) {
try {
try {
userAuth.signalAuthMethodFailure(
session, service, partial,
Collections.unmodifiableList(serverMethods), buffer);
} finally {
userAuth.destroy();
}
} finally {
userAuth = null;
}
}
} tryNext(cmd);
return;
}
...
}{code}
{code:java}
protected void tryNext(int cmd) throws Exception {
ClientSession session = getClientSession();
// Loop until we find something to try
for (boolean debugEnabled = log.isDebugEnabled();; debugEnabled =
log.isDebugEnabled()) {
...
String method = null;
for (; currentMethod < clientMethods.size(); currentMethod++) {
method = clientMethods.get(currentMethod); // Always selects the
0th client method when the previous authentication method was "partially
successful"
if (serverMethods.contains(method)) {
break;
}
}
...
}
} {code}
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