What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-22

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 products

• ronf asyncssh: before 2.23.1

References

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

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