{"id":"UBUNTU-CVE-2026-62949","details":"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.","modified":"2026-09-18T12:30:36.772343915Z","published":"2026-09-18T00:00:00Z","upstream":["CVE-2026-62949"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-62949"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-62949"},{"type":"REPORT","url":"https://github.com/ronf/asyncssh/commit/756cbae5350789ce9735f15f704bae9b5a3608b8"},{"type":"REPORT","url":"https://github.com/ronf/asyncssh/commit/9c354270c009285525e126721e8ed5fbed1f8a67"},{"type":"REPORT","url":"https://github.com/ronf/asyncssh/releases/tag/v2.24.0"},{"type":"REPORT","url":"https://github.com/ronf/asyncssh/security/advisories/GHSA-rw4j-r22c-9gc3"}],"affected":[{"package":{"name":"python-asyncssh","ecosystem":"Ubuntu:16.04:LTS","purl":"pkg:deb/ubuntu/python-asyncssh?arch=source&distro=xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.2.0-1","1.2.1-1","1.3.0-1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.3.0-1","binary_name":"python3-asyncssh"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/python-asyncssh?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.1-2","1.11.0-2","1.11.1-1","1.11.1-1ubuntu0.1~esm1","1.11.1-1ubuntu0.1~esm2"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-asyncssh","binary_version":"1.11.1-1ubuntu0.1~esm2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/python-asyncssh?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.12.2-1","1.12.2-1ubuntu0.1","1.12.2-1ubuntu0.2"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-asyncssh","binary_version":"1.12.2-1ubuntu0.2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/python-asyncssh?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.5.0-1","2.5.0-1ubuntu0.1~esm1","2.5.0-1ubuntu0.1","2.5.0-1ubuntu0.1+esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-asyncssh","binary_version":"2.5.0-1ubuntu0.1+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/python-asyncssh?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.10.1-2","2.10.1-2ubuntu0.1","2.10.1-2ubuntu0.1+esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-asyncssh","binary_version":"2.10.1-2ubuntu0.1+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/python-asyncssh?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.20.0-1","2.21.1-1"],"ecosystem_specific":{"binaries":[{"binary_version":"2.21.1-1","binary_name":"python3-asyncssh"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-62949.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"},{"type":"Ubuntu","score":"medium"}]}