tomaswolf commented on code in PR #449:
URL: https://github.com/apache/mina-sshd/pull/449#discussion_r1442183563
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sshd-core/src/main/java/org/apache/sshd/common/session/helpers/AbstractSession.java:
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@@ -2056,11 +2128,33 @@ protected Map<KexProposalOption, String> negotiate()
throws Exception {
Map<KexProposalOption, String> s2cOptions = getServerKexProposals();
signalNegotiationStart(c2sOptions, s2cOptions);
+ // Make modifiable. Strict KEX flags are to be heeded only in initial
KEX, and to be ignored afterwards.
+ c2sOptions = new EnumMap<>(c2sOptions);
+ s2cOptions = new EnumMap<>(s2cOptions);
+ boolean strictKexClient = removeValue(c2sOptions,
KexProposalOption.ALGORITHMS,
+ KexExtensions.STRICT_KEX_CLIENT_EXTENSION);
+ boolean strictKexServer = removeValue(s2cOptions,
KexProposalOption.ALGORITHMS,
+ KexExtensions.STRICT_KEX_SERVER_EXTENSION);
+ // Make unmodifiable again
+ c2sOptions = Collections.unmodifiableMap(c2sOptions);
+ s2cOptions = Collections.unmodifiableMap(s2cOptions);
Map<KexProposalOption, String> guess = new
EnumMap<>(KexProposalOption.class);
Map<KexProposalOption, String> negotiatedGuess =
Collections.unmodifiableMap(guess);
try {
boolean debugEnabled = log.isDebugEnabled();
boolean traceEnabled = log.isTraceEnabled();
+ if (!initialKexDone) {
+ strictKex = strictKexClient && strictKexServer;
+ if (debugEnabled) {
+ log.debug("negotiate({}) strict KEX={} client={}
server={}", this, strictKex, strictKexClient,
+ strictKexServer);
+ }
+ if (strictKex && initialKexInitSequenceNumber != 1) {
+ throw new
SshException(SshConstants.SSH2_DISCONNECT_KEY_EXCHANGE_FAILED,
+ "Strict KEX negotiated but sequence number of
first KEX_INIT received is not 1: "
+
+ initialKexInitSequenceNumber);
+ }
+ }
Review Comment:
You mean, a client sending the server flag or vice versa?
<s>You're right, we must remove those, too, otherwise we might end up
negotiating it as a kex algorithm :-)</s>
Actually, no. In the worst case, the client proposal will be left with the
server flag, and the server proposal with the client flag. They'll just be
ignored, and will never be negotiated as kex algorithm. But it seems safer to
remove and log them anyway.
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