---
id: CVE-2026-62949
title: >-
  AsyncSSH is a Python package which provides an asynchronous client and server
  implementation of the SSHv2 protocol on top of the Python asyncio framework
summary: >-
  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 a…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-835
vendor: ronf
product: asyncssh
affected:
  - asyncssh < 2.24.0
patched:
  - asyncssh 2.24.0
published: '2026-09-16'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T16:17:34.413'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-62949'
references:
  - url: >-
      https://github.com/ronf/asyncssh/commit/756cbae5350789ce9735f15f704bae9b5a3608b8
    label: security-advisories@github.com
  - url: >-
      https://github.com/ronf/asyncssh/commit/9c354270c009285525e126721e8ed5fbed1f8a67
    label: security-advisories@github.com
  - url: 'https://github.com/ronf/asyncssh/releases/tag/v2.24.0'
    label: security-advisories@github.com
  - url: 'https://github.com/ronf/asyncssh/security/advisories/GHSA-rw4j-r22c-9gc3'
    label: security-advisories@github.com
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-62949'
  - url: 'https://github.com/advisories/GHSA-rw4j-r22c-9gc3'
  - url: 'https://github.com/ronf/asyncssh'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-62949.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-62949'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2535643'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-62949'
tags:
  - nvd
  - cve.org
  - ghsa
  - pip
  - osv
  - csaf
  - vex
  - red-hat
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-17T15:01:41.382412Z'
aliases:
  - GHSA-rw4j-r22c-9gc3
ecosystem: pip
ingestedAt: '2026-09-16T21:05:36.875Z'
epss: 0.00548
epssPercentile: 0.43531
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-62949)

Affected packages:

- `asyncssh <= 2.23.1`

Patched in:

- `asyncssh 2.24.0`

Source: https://github.com/advisories/GHSA-rw4j-r22c-9gc3

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Ceph Storage 7, Red Hat Ceph Storage 8, Red Hat Ceph Storage 9 · no fix planned: Red Hat Ceph Storage 7, Red Hat Ceph Storage 8, Red Hat Ceph Storage 9 · updated 2026-09-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-62949.json)