Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A flaw was found in libssh channel handling. In ssh_packet_channel_open() in src/messages.c and ssh_packet_channel_open_conf() in src/channels.c, the implementation accepts a peer-controlled maximum packet size of 0 in channel open messages. That zero value is stored in channel state and later reaches channel_write_common(), where forward progress depends on the remote maximum packet size being positive; with 0, the remaining length is never reduced and the write path loops indefinitely, consuming CPU and causing denial of service. A remote authenticated peer can trigger this by advertising a zero maximum packet size in SSH_MSG_CHANNEL_OPEN or SSH_MSG_CHANNEL_OPEN_CONFIRMATION.