CVE-2026-62949
AsyncSSH: asyncio event-loop freeze via SSH maximum packet size = 0 in SSH_MSG_CHANNEL_OPEN / OPEN_CONFIRMATION
No known exploitation. EPSS puts it in the 43rd percentile. No fix published yet.
What to do
No fixed build or workaround is published yet. Limit exposure and watch for a patch.
What it is
From the CVE record
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.
In plain language
No plain-language summary for this CVE yet.
Exploitation
Where each signal puts this CVE on the scale from published to confirmed exploited.
- CISA KEV
Not in the catalog. CISA has not confirmed exploitation.
- Public exploits
No public exploit or proof of concept found in the sources we track.
- EPSS
0.5% chance of exploitation activity in the next 30 days, which ranks it in the 43rd percentile of scored CVEs.
Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.
Lifecycle
5 events over 1 day, from the signal feeds we watch.
- Record updated
- Publishedweakness classified, att&ck mapped, record updated
Affected products
Technical detail
CVSS 3.1 vector
Open in the CVSS calculatorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Scored 6.5 by NVD.
How it is reached
- Attack Vector NetworkExploitable remotely over the network without any special conditions
- Attack Complexity LowNo special conditions — the attack can be reliably reproduced
- Privileges Required LowRequires basic user-level privileges
- User Interaction NoneNo user interaction needed — fully automated exploitation
Scope
- Scope UnchangedImpact is limited to the vulnerable component itself
Impact if exploited
- Confidentiality NoneNo confidentiality impact
- Integrity NoneNo integrity impact
- Availability HighTotal denial of service — the component is completely unavailable
Weaknesses
ATT&CK techniques
Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.
Sources
Watch the software you run.
My Stack ranks new CVEs for your products by real-world exploitation, so the next serious one reaches you without reading every advisory.
We'll flag the next CVE, public exploit or patch for Asyncssh, not every advisory.
A free account adds
- The full version matrix and every affected product
- Exploit links, proofs of concept and Metasploit modules
- Email alerts for the products you watch
- The same data over REST API, MCP and CLI