handleData subtracts the length of every data packet from the receive
window, but extended data with a type code other than
SSH2_EXTENDED_DATA_STDERR is then silently discarded and, since no API
exists to read it, its window credit was never returned: adjustWindow
only runs as a side effect of reading a stream. A peer sending
extended data with an unknown type code could therefore permanently
shrink the channel window, down to a complete stall of the channel.
Credit the discarded bytes back through adjustWindow. adjustWindow
returns io.EOF if the local side has already sent a channel close;
ignore it like ReadExtended does, since an error returned here would
terminate the mux read loop and tear down the whole connection. For
comparison, OpenSSH rejects extended data with unexpected type codes
outright and never buffers it, so the dropped bytes are simply never
credited back to the misbehaving peer.
Fixesgolang/go#80333
Change-Id: Ia311ce3ad008e7c89ce9752f1937c91374a4e74f
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/802901
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
The internal 'min' helper function in channel.go incorrectly cast the
input data length (int) to uint32 before comparing it with the
maximum packet size. On 64-bit systems, if the data length is a
multiple of 2^32 (approx. 4GB), this cast results in 0.
Consequently, the function returns 0, causing the WriteExtended loop
to spin indefinitely because it attempts to reserve 0 bytes while
the remaining data length is still positive.
This change renames the helper to 'minPayloadSize' to avoid confusion
with the Go 1.21 built-in 'min' and updates the logic to use int64
for comparisons, preventing truncation and the resulting infinite loop.
This issue was found during a security audit by NCC Group Cryptography
Services, sponsored by Teleport.
Fixesgolang/go#79567
Fixes CVE-2026-39834
Change-Id: Id5bf81d9f06c7042452acffe1c76580ff878665e
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/781663
Reviewed-by: Neal Patel <nealpatel@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Nicola Murino