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

> Attackers can bypass authorized keys directory restrictions via tilde or environment variable expansion in AsyncSSH, potentially reading sensitive files.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Jul 2026
- **Updated:** 10 Jul 2026
- **Also known as:** CLEANSTART-2026-IL04203, DEBIAN-CVE-2026-54590, ECHO-3b00-f8ea-bea7, GHSA-qr67-gv47-xwwh, MINI-56v4-gf5f-fxwp, MINI-c428-pwrv-rr6c, MINI-ff97-66g9-mwgh, PYSEC-2026-3809, UBUNTU-CVE-2026-54590

## What is CVE-2026-54590?

CVE-2026-54590 is a medium-severity path traversal vulnerability in ronf asyncssh, published on 8 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. 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.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-54590?

3 open source packages ship an affected version, including asyncssh.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `asyncssh` | PyPI | All versions | 2.23.1 |
| `asyncssh` | PyPI | All versions | 2.23.1 |
| `asyncssh` | PyPI | All versions | 2.23.1 |

## How do I fix CVE-2026-54590?

Upgrade asyncssh to 2.23.1 or later.

## Is CVE-2026-54590 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54590 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54590 and fix it if it is affected.

What it is: CVE-2026-54590 is a medium-severity path traversal vulnerability in ronf asyncssh, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54590 exists.

Affected packages and fixed versions:
- asyncssh (PyPI): affected all versions; fixed in 2.23.1
- asyncssh (PyPI): affected all versions; fixed in 2.23.1
- asyncssh (PyPI): affected all versions; fixed in 2.23.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54590/ (Markdown: https://insights.sbomify.com/CVE-2026-54590/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54590
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54590
- OSV: https://osv.dev/vulnerability/CVE-2026-54590

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54590/
Summaries are generated and may contain mistakes; the official description above is the record.