ronf asyncssh up to 2.23.x Channel asyncssh/connection.py send_pktsize infinite loop

Summaryinfo

A vulnerability was found in ronf asyncssh up to 2.23.x. It has been declared as problematic. This impacts the function _process_channel_open/_process_channel_open_confirmation of the file asyncssh/connection.py of the component Channel Handler. Such manipulation of the argument send_pktsize leads to infinite loop. This vulnerability is listed as CVE-2026-62949. The attack may be performed from remote. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in ronf asyncssh up to 2.23.x. Affected by this issue is the function _process_channel_open/_process_channel_open_confirmation of the file asyncssh/connection.py of the component Channel Handler. The manipulation of the argument send_pktsize with an unknown input leads to a infinite loop vulnerability. Using CWE to declare the problem leads to CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. Impacted is availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-62949 since 07/15/2026. The exploitation is known to be easy. The attack may be launched remotely. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

Upgrading to version 2.24.0 eliminates this vulnerability.

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Productinfo

Vendor

• ronf

Name

• asyncssh

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9
• 2.10
• 2.11
• 2.12
• 2.13
• 2.14
• 2.15
• 2.16
• 2.17
• 2.18
• 2.19
• 2.20
• 2.21
• 2.22
• 2.23

Website

• Product: https://github.com/ronf/asyncssh/

CPE 2.3info

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