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| author | Peter Verraedt <peter@verraedt.be> | 2022-03-21 12:44:56 +0000 |
|---|---|---|
| committer | Filippo Valsorda <filippo@golang.org> | 2022-03-21 15:39:16 +0000 |
| commit | 2c7772ba30643b7a2026cbea938420dce7c6384d (patch) | |
| tree | e42e2e09a4fc622fa6ea023613eaf6329721486e | |
| parent | 3147a52a75dda54ac3a611ef8978640d85188a2a (diff) | |
| download | go-x-crypto-2c7772ba30643b7a2026cbea938420dce7c6384d.tar.xz | |
ssh: send ext-info-c only once
In accordance to RFC8308, send ext-info-c only during the first key
exchange. Some server implementations such as OpenSSH 7 will send an
extInfoMsg message each time when ext-info-c is received. This results
in a closed connection, as our client does not expect this message while
handling the mux.
See https://bugzilla.mindrot.org/show_bug.cgi?id=2929 regarding the
behaviour of OpenSSH if it sees ext-info-c in later key exchanges.
Fixes golang/go#51808
Change-Id: Id94f1ef73cec6147136246b0b6048b57db92660d
GitHub-Last-Rev: fcfe5ed37306136219854031abc809e0dc9b3124
GitHub-Pull-Request: golang/crypto#208
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/394134
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Trust: Roland Shoemaker <roland@golang.org>
| -rw-r--r-- | ssh/handshake.go | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/ssh/handshake.go b/ssh/handshake.go index f815cdb..653dc4d 100644 --- a/ssh/handshake.go +++ b/ssh/handshake.go @@ -479,10 +479,12 @@ func (t *handshakeTransport) sendKexInit() error { // As a client we opt in to receiving SSH_MSG_EXT_INFO so we know what // algorithms the server supports for public key authentication. See RFC - // 8303, Section 2.1. - msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+1) - msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...) - msg.KexAlgos = append(msg.KexAlgos, "ext-info-c") + // 8308, Section 2.1. + if firstKeyExchange := t.sessionID == nil; firstKeyExchange { + msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+1) + msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...) + msg.KexAlgos = append(msg.KexAlgos, "ext-info-c") + } } packet := Marshal(msg) |