UBUNTU-CVE-2026-62949 (CVE-2026-62949)
Vulnerability from osv_ubuntu – Published: 2026-09-16 20:17 – Updated: 2026-09-23 23:31 – Source website
VLAI
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.
Severity
6.5 (Medium)
N/A (UNKNOWN)
References
{
"affected": [
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-asyncssh",
"binary_version": "1.3.0-1"
}
]
},
"package": {
"ecosystem": "Ubuntu:16.04:LTS",
"name": "python-asyncssh",
"purl": "pkg:deb/ubuntu/python-asyncssh@1.3.0-1?arch=source\u0026distro=xenial"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.2.0-1",
"1.2.1-1",
"1.3.0-1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-asyncssh",
"binary_version": "1.11.1-1ubuntu0.1~esm2"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:18.04:LTS",
"name": "python-asyncssh",
"purl": "pkg:deb/ubuntu/python-asyncssh@1.11.1-1ubuntu0.1~esm2?arch=source\u0026distro=esm-apps/bionic"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"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": "1.12.2-1ubuntu0.2"
}
]
},
"package": {
"ecosystem": "Ubuntu:20.04:LTS",
"name": "python-asyncssh",
"purl": "pkg:deb/ubuntu/python-asyncssh@1.12.2-1ubuntu0.2?arch=source\u0026distro=focal"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.12.2-1",
"1.12.2-1ubuntu0.1",
"1.12.2-1ubuntu0.2"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-asyncssh",
"binary_version": "2.5.0-1ubuntu0.1+esm1"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:22.04:LTS",
"name": "python-asyncssh",
"purl": "pkg:deb/ubuntu/python-asyncssh@2.5.0-1ubuntu0.1+esm1?arch=source\u0026distro=esm-apps/jammy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"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": "2.10.1-2ubuntu0.1+esm1"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:24.04:LTS",
"name": "python-asyncssh",
"purl": "pkg:deb/ubuntu/python-asyncssh@2.10.1-2ubuntu0.1+esm1?arch=source\u0026distro=esm-apps/noble"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"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": "2.21.1-1"
}
]
},
"package": {
"ecosystem": "Ubuntu:26.04:LTS",
"name": "python-asyncssh",
"purl": "pkg:deb/ubuntu/python-asyncssh@2.21.1-1?arch=source\u0026distro=resolute"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.20.0-1",
"2.21.1-1"
]
}
],
"aliases": [],
"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.",
"id": "UBUNTU-CVE-2026-62949",
"modified": "2026-09-23T23:31:26Z",
"published": "2026-09-16T20:17:00Z",
"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"
}
],
"related": [],
"schema_version": "1.7.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "medium",
"type": "Ubuntu"
}
],
"upstream": [
"CVE-2026-62949"
]
}
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Browse all ATT&CK techniques and the vulnerabilities related to each.
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