{"id":"CVE-2026-62949","summary":"AsyncSSH: asyncio event-loop freeze via SSH maximum packet size = 0 in SSH_MSG_CHANNEL_OPEN / OPEN_CONFIRMATION","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.","aliases":["GHSA-rw4j-r22c-9gc3"],"modified":"2026-09-19T03:30:43.051124626Z","published":"2026-09-16T20:00:46.657Z","database_specific":{"cna_assigner":"GitHub_M","cwe_ids":["CWE-835"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/62xxx/CVE-2026-62949.json"},"references":[{"type":"WEB","url":"https://github.com/ronf/asyncssh/releases/tag/v2.24.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/62xxx/CVE-2026-62949.json"},{"type":"ADVISORY","url":"https://github.com/ronf/asyncssh/security/advisories/GHSA-rw4j-r22c-9gc3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-62949"},{"type":"FIX","url":"https://github.com/ronf/asyncssh/commit/756cbae5350789ce9735f15f704bae9b5a3608b8"},{"type":"FIX","url":"https://github.com/ronf/asyncssh/commit/9c354270c009285525e126721e8ed5fbed1f8a67"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ronf/asyncssh","events":[{"introduced":"0"},{"fixed":"756cbae5350789ce9735f15f704bae9b5a3608b8"},{"fixed":"9c354270c009285525e126721e8ed5fbed1f8a67"},{"fixed":"3577224af6489a8c2653ce5b60dccfa5979f5ce0"}],"database_specific":{"source":["AFFECTED_FIELD","REFERENCES"],"extracted_events":[{"introduced":"0"},{"fixed":"2.24.0"}]}}],"versions":["v2.24.0","v2.23.1","v2.23.0","v2.22.0","v2.21.1","v2.21.0","v2.20.0","v2.19.0","v2.18.0","v2.17.0","v2.16.0","v2.15.0","v2.14.2","v2.14.1","v2.14.0","v2.13.2","v2.13.1","v2.13.0","v2.12.0","v2.11.0","v2.10.1","v2.10.0","v2.9.0","v2.8.1","v2.8.0","v2.7.2","v2.7.1","v2.7.0","v2.6.0","v2.5.0","v2.4.2","v2.4.1","v2.4.0","v2.3.0","v2.2.1","v2.2.0","v2.1.0","v2.0.1","v2.0.0","v1.18.0","v1.17.1","v1.17.0","v1.16.1","v1.16.0","v1.15.1","v1.15.0","v1.14.0","v1.13.3","v1.13.2","v1.13.1","v1.13.0","v1.12.2","v1.12.1","v1.12.0","v1.11.1","v1.11.0","v1.10.1","v1.10.0","v1.9.0","v1.8.1","v1.8.0","v1.7.3","v1.7.2","v1.7.1","v1.6.2","v1.6.1","v1.6.0","v1.5.6","v1.5.5","v1.5.4","v1.5.3","v1.5.2","v1.5.1","v1.5.0","v1.4.1","v1.4.0","v1.3.2","v1.3.1","v1.3.0","v1.2.1","v1.2.0","v1.1.1","v1.1.0","v1.0.1","v1.0.0","v0.9.2","v0.9.1","v0.9.0","v0.8.4","v0.8.3","v0.8.2","v0.8.1","v0.8.0","v0.7.0","v0.6.0","v0.5.0","v0.4.0","v0.3.0","v0.2.0","v0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/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"}]}