DEBIAN-CVE-2026-116774: Medium severity debian/rust-russh vulnerability

russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. From 0.60.0 until 0.65.0, channel-open parsing accepts a peer-declared maximumpacketsize of zero and passes it into ChannelTx::pollwritable in russh/src/channels/io/tx.rs. The Channel::data, Channel::makewriter, and Channel::intostream asynchronous write paths then calculate a writable size of zero and remain pending forever because window adjustments cannot satisfy a static zero packet maximum. An authenticated client can strand server writes, and a malicious server can strand client writes, allowing affected tasks, channels, and connections to accumulate without surfacing an error. This issue is fixed in version 0.65.0.