Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-54590AsyncSSH AuthorizedKeysFile username substitution bypass through ~ and environment expansion

Medium 5.9

In plain English

A medium-severity path traversal in asyncssh from ronf. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium

Exploit odds (30 days)0.3%top 72.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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. 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	python-asyncssh	2.24.0-1	DEBIAN-CVE-2026-54590
PyPI	asyncssh	2.23.1	GHSA-qr67-gv47-xwwh
PyPI	asyncssh	2.23.1	PYSEC-2026-3809
Ubuntu:25.10	python-asyncssh	no fix listed	UBUNTU-CVE-2026-54590
Ubuntu:26.04:LTS	python-asyncssh	no fix listed	UBUNTU-CVE-2026-54590
Ubuntu:26.10	python-asyncssh	no fix listed	UBUNTU-CVE-2026-54590

Affected products (as reported)

Vendor	Product	Versions
ronf	asyncssh	< 2.23.1

Weakness: CWE-22, CWE-639 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

References

https://github.com/ronf/asyncssh/security/advisories/GHSA-qr67-gv47-xwwh x_refsource_CONFIRM
https://github.com/ronf/asyncssh/commit/3d515ba9ba0cd9990d248bdf62bcf05d51261a88 x_refsource_MISC
https://github.com/ronf/asyncssh/releases/tag/v2.23.1 x_refsource_MISC