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asyncssh · Vulnerability

CVSS 3.1 6.5 MEDIUMCheck source for fixed versionsKEV status unknown

cve-program · CVE-2026-62949

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-62949

Published

asyncssh

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "ronf",
                    "product": "asyncssh",
                    "versions": [
                        {
                            "version": "< 2.24.0",
                            "status": "affected"
                        }
                    ]
                }

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ChangeIntel

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Sources read 13 Nov 08:15 UTC · 274 of 275 readable · 272 fully read · documentation 469/469 current