CVE-2026-62949

Name	CVE-2026-62949
Description	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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1148448

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-asyncssh (PTS)	bookworm	2.10.1-2+deb12u2	vulnerable
	bookworm (security)	2.10.1-2+deb12u1	vulnerable
	trixie	2.20.0-1	vulnerable
	forky, sid	2.24.0-2	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-asyncssh	source	(unstable)	(unfixed)			1148448

Notes

[trixie] - python-asyncssh <no-dsa> (Minor issue)
https://github.com/ronf/asyncssh/security/advisories/GHSA-rw4j-r22c-9gc3
https://github.com/ronf/asyncssh/commit/9c354270c009285525e126721e8ed5fbed1f8a67 (v2.24.0)
https://github.com/ronf/asyncssh/commit/756cbae5350789ce9735f15f704bae9b5a3608b8
Followup commit not in 2.24, should be included when fixing the issue