AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework

Overview

AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Prior to 2.24.0, _process_channel_open and _process_channel_open_confirmation in asyncssh/connection.py accept a peer-supplied send_pktsize value of zero. When channel data reaches SSHChannel._flush_send_buf in asyncssh/channel.py, the zero value causes each loop iteration to slice and remove zero bytes without reducing the send window, leaving the synchronous loop permanently true with no await point. A malicious SSH server can trigger the client path through SSH_MSG_CHANNEL_OPEN_CONFIRMATION before the first channel write, while an authenticated client can trigger the server path through SSH_MSG_CHANNEL_OPEN and freeze every current and future connection handled by the process. This vulnerability is fixed in 2.24.0.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Package advisory (CVE-2026-62949)

Affected packages:

• asyncssh <= 2.23.1

Patched in:

• asyncssh 2.24.0

Source: https://github.com/advisories/GHSA-rw4j-r22c-9gc3

Vendor advisories

• Red Hat VEX · Moderate · affected: Red Hat Ceph Storage 7, Red Hat Ceph Storage 8, Red Hat Ceph Storage 9 · no fix planned: Red Hat Ceph Storage 9, Red Hat Ceph Storage 7, Red Hat Ceph Storage 8 · updated 2026-09-16 · vex