{"cve":"CVE-2026-62949","nvd":{"published":"2026-09-16T20:17:26.220","modified":"2026-09-30T17:43:24.057","status":"Awaiting Analysis","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":6.5},"cwes":["CWE-835"],"references":["https://github.com/ronf/asyncssh/commit/756cbae5350789ce9735f15f704bae9b5a3608b8","https://github.com/ronf/asyncssh/commit/9c354270c009285525e126721e8ed5fbed1f8a67","https://github.com/ronf/asyncssh/releases/tag/v2.24.0","https://github.com/ronf/asyncssh/security/advisories/GHSA-rw4j-r22c-9gc3"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:54:41.405518556+00:00"},"epss":{"cve":"CVE-2026-62949","score":0.00389,"percentile":0.32717,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-rw4j-r22c-9gc3","url":"https://osv.dev/vulnerability/GHSA-rw4j-r22c-9gc3","summary":"AsyncSSH: asyncio event-loop freeze via SSH maximum packet size = 0 in SSH_MSG_CHANNEL_OPEN / OPEN_CONFIRMATION","modified":"2026-10-01T17:55:57.395536709Z","packages":[{"ecosystem":"PyPI","name":"asyncssh","purl":"pkg:pypi/asyncssh","ranges":["<2.24.0"],"fixed":["2.24.0"]}]},{"id":"PYSEC-2026-4026","url":"https://osv.dev/vulnerability/PYSEC-2026-4026","summary":"AsyncSSH: asyncio event-loop freeze via SSH maximum packet size = 0 in SSH_MSG_CHANNEL_OPEN / OPEN_CONFIRMATION","modified":"2026-10-01T17:45:03.138454039Z","packages":[{"ecosystem":"PyPI","name":"asyncssh","purl":"pkg:pypi/asyncssh","ranges":["<2.24.0"],"fixed":["2.24.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}