Medium severity · published Jul 8, 2026
CVE-2026-54590
AsyncSSH AuthorizedKeysFile username substitution bypass through ~ and environment expansion
5.9
CVSS
0.3%
EPSS
No
On KEV
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. Version 2.23.0 contains an incomplete fix for CVE-2026-45309 in SSHServerConfig._set_tokens that blocks /, , and .. before %u substitution in AuthorizedKeysFile but does not block a leading ~ or ${ENV}, allowing later expansion in _expand_val and Path(filename).expanduser() to escape the intended authorized-keys directory. This issue is fixed in version 2.23.1.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 27% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
AS
asyncssh · ronf
< 2.23.1 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-54590
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-54590
github.com
https://github.com/ronf/asyncssh/commit/3d515ba9ba0cd9990d248bdf62bcf05d51261a88
github.com
https://github.com/ronf/asyncssh/releases/tag/v2.23.1
github.com
https://github.com/ronf/asyncssh/security/advisories/GHSA-qr67-gv47-xwwh
More from asyncssh
8.1
CVE-2026-54591
AsyncSSH: SCP Path Traversal to Arbitrary File Write
7.5
CVE-2026-45309
AsyncSSH `AuthorizedKeysFile %u` path traversal allows attacker-selected authorized keys to authenticate a traversal username
6.5
CVE-2026-62949
AsyncSSH: asyncio event-loop freeze via SSH maximum packet size = 0 in SSH_MSG_CHANNEL_OPEN / OPEN_CONFIRMATION