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GHSA-h5rc-j5f5-3gcm
No affected components available
Summary
The channel window adjust message of the SSH protocol is used to track the free space in the receive buffer of the other side of a channel. The current implementation takes the value from the message and adds it to an internal state value. This can result in a integer overflow. If the Rust code is compiled with overflow checks, it will panic. A malicious client can crash a server.
Details
According https://datatracker.ietf.org/doc/html/rfc4254#section-5.2, The value must not overflow. The incorrect handling is done in server/encrypted.rs and client/encrypted.rs in the handling of CHANNEL_WINDOW_ADJUST.
let amount = map_err!(u32::decode(&mut r))?;
...
channel.recipient_window_size += amount;
It could be replaced with something like
if let Some(ref mut channel) = enc.channels.get_mut(&channel_num) {
// rfc 4254: The window MUST NOT be increased above 2^32 - 1 bytes.
new_size = channel.recipient_window_size.saturating_add(amount);
channel.recipient_window_size = new_size;
}
...
PoC
A customized client code would be required to send a message with a big value like u32_max. Not done yet.
Impact
This problem seems only critical to a server. One user can crash the server, which might take down the service. A malicious server could also crash a single client, but this seems not very critical.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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