CVE-2026-62949: CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') in ronf asyncssh
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.
AI Analysis
Technical Summary
AsyncSSH, a Python package implementing SSHv2 asynchronously, has a vulnerability (CVE-2026-62949) where the functions _process_channel_open and _process_channel_open_confirmation accept a peer-supplied send_pktsize value of zero. This zero value causes the SSHChannel._flush_send_buf method to enter an infinite loop by repeatedly slicing zero bytes without reducing the send window, resulting in a synchronous loop with no await points. A malicious SSH server can exploit this on the client side via SSH_MSG_CHANNEL_OPEN_CONFIRMATION before the first channel write, while an authenticated client can exploit the server side via SSH_MSG_CHANNEL_OPEN, freezing all current and future connections handled by the process. The vulnerability is resolved in AsyncSSH version 2.24.0.
Potential Impact
The vulnerability leads to an infinite loop causing denial of service by freezing the affected AsyncSSH client or server process. It does not impact confidentiality or integrity but results in availability loss. Both client and server implementations are affected prior to version 2.24.0.
Mitigation Recommendations
Upgrade AsyncSSH to version 2.24.0 or later, where this infinite loop vulnerability is fixed. No other mitigations are indicated.
CVE-2026-62949: CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') in ronf asyncssh
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 v3.1
Score 6.5medium
Affected software
ronf
asyncssh
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
AsyncSSH, a Python package implementing SSHv2 asynchronously, has a vulnerability (CVE-2026-62949) where the functions _process_channel_open and _process_channel_open_confirmation accept a peer-supplied send_pktsize value of zero. This zero value causes the SSHChannel._flush_send_buf method to enter an infinite loop by repeatedly slicing zero bytes without reducing the send window, resulting in a synchronous loop with no await points. A malicious SSH server can exploit this on the client side via SSH_MSG_CHANNEL_OPEN_CONFIRMATION before the first channel write, while an authenticated client can exploit the server side via SSH_MSG_CHANNEL_OPEN, freezing all current and future connections handled by the process. The vulnerability is resolved in AsyncSSH version 2.24.0.
Potential Impact
The vulnerability leads to an infinite loop causing denial of service by freezing the affected AsyncSSH client or server process. It does not impact confidentiality or integrity but results in availability loss. Both client and server implementations are affected prior to version 2.24.0.
Mitigation Recommendations
Upgrade AsyncSSH to version 2.24.0 or later, where this infinite loop vulnerability is fixed. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-14T22:32:17.731Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6aaaf94455bf5e2cf51ba045
Added to database: 09/16/2026, 20:17:08 UTC
Last enriched: 09/16/2026, 20:32:11 UTC
Last updated: 09/17/2026, 04:15:32 UTC
Views: 7
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