# AsyncSSH: asyncio event-loop freeze via SSH maximum packet size = 0 in SSH_MSG_CHANNEL_OPEN / OPEN_CONFIRMATION

Advisory record · `GHSA-rw4j-r22c-9gc3`

- **Identifiers:** `GHSA-rw4j-r22c-9gc3` · `CVE-2026-62949` · `PYSEC-2026-4026`
- **State:** Confirmed
- **Severity:** CVSS 6.5 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-835](https://cwe.mitre.org/data/definitions/835.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 17 Sept 2026
- **Updated:** 1 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 17 Sept 2026, 14:53 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `asyncssh` (PyPI): affected `<2.24.0`; fixed in `2.24.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> AsyncSSH versions before 2.24.0 are vulnerable to an event-loop freeze when a channel maximum packet size of 0 is accepted. A malicious SSH server can trigger this against a client, and an authenticated client can trigger it against a server, which then blocks all connections. Upgrade to AsyncSSH 2.24.0 or later.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.5 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0039, the 33rd percentile, on 13 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:09 UTC: First seen by agentprime
- 31 Oct 2026, 14:09 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-rw4j-r22c-9gc3)

## Sources

- [GitHub Advisory Database: GHSA-rw4j-r22c-9gc3](https://github.com/advisories/GHSA-rw4j-r22c-9gc3)
- [OSV: GHSA-rw4j-r22c-9gc3](https://osv.dev/vulnerability/GHSA-rw4j-r22c-9gc3)
- <https://github.com/ronf/asyncssh/security/advisories/GHSA-rw4j-r22c-9gc3>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-62949>
- <https://github.com/ronf/asyncssh/commit/756cbae5350789ce9735f15f704bae9b5a3608b8>
- <https://github.com/ronf/asyncssh/commit/9c354270c009285525e126721e8ed5fbed1f8a67>
- <https://github.com/ronf/asyncssh>
- <https://github.com/ronf/asyncssh/releases/tag/v2.24.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-rw4j-r22c-9gc3>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-rw4j-r22c-9gc3/>. Everything for agents: <https://agentprime.io/llms.txt>.