CVE-2026-54590 is a medium-severity (CVSS 5.9) Path Traversal vulnerability in asyncssh. O3 Security confirms whether CVE-2026-54590 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
AsyncSSH AuthorizedKeysFile username substitution bypass through ~ and environment expansion
Real-World Exposure
asyncsshReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | asyncssh | all versions | 2.23.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for asyncssh. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update asyncssh to 2.23.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54590 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-54590 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-54590. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-54590 in your dependencies?
O3 detects CVE-2026-54590 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.