ecki commented on code in PR #449:
URL: https://github.com/apache/mina-sshd/pull/449#discussion_r1442207857
##########
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:
Yeah right,that what’s the additional list was used for. I think it’s not
critical to not remove it (since you filter your own side) but it’s probably
better to handle the case (with a comment). The rfc8308 verbage (for
ext-info-*) would allow to disconnect or ignore for malicious/illegal offers:
> Implementations MUST NOT send an incorrect indicator name for their
role. Implementations MAY disconnect if the counterparty sends an
incorrect indicator. If "ext-info-c" or "ext-info-s" ends up being
negotiated as a key exchange method, the parties MUST disconnect.
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