CVE-2026-45309 AsyncSSH `AuthorizedKeysFile %u` path traversal allows attacker-selected authorized keys to authenticate a traversal username
Attackers can authenticate using arbitrary key files via path traversal in AsyncSSH when AuthorizedKeysFile uses the %u token.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45309?
CVE-2026-45309 is a high-severity path traversal vulnerability in ronf asyncssh, published on 17 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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 2.23.0, AsyncSSH expands the OpenSSH-compatible AuthorizedKeysFile %u token in asyncssh/config.py, asyncssh/connection.py, asyncssh/auth_keys.py, and asyncssh/misc.py with the raw SSH username during pre-authentication server config reload, allowing a server configured with AuthorizedKeysFile authorized_keys/%u to read an authorized-keys file outside the intended directory when the SSH username contains /, \, or .. path traversal segments and authenticate with an attacker-selected key file. This issue is fixed in version 2.23.0.
Weakness: CWE-22
Which versions are affected by CVE-2026-45309?
3 open source packages ship an affected version, including asyncssh. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
asyncssh PyPI | From 2.22.0 | 2.23.0 |
asyncssh PyPI | From 2.22.0 | 2.23.0 |
asyncssh PyPI | From 2.22.0 | 2.23.0 |
Linux distribution packages (1)
python-asyncssh openSUSE:Tumbleweed | All versions | 2.23.1-1.1 |
Products include Asyncssh Project Asyncssh.
How do I fix CVE-2026-45309?
Upgrade asyncssh to 2.23.0 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-45309 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45309 exists.
Other vulnerabilities in ronf asyncssh
Sources
Also known as CLEANSTART-2026-UM40247, CLEANSTART-2026-WV96741, DEBIAN-CVE-2026-45309, ECHO-478b-8ec8-3dc3, GHSA-g794-3fmp-753h, MINI-4ggg-6rv9-j647 and 4 more.