asyncssh has SCP Path Traversal to Arbitrary File Write
| Product | asyncssh (all versions through 2.23.0) |
| Related | CVE-2019-6111 (same class in OpenSSH) |
| Fix | AsyncSSH 2.23.1 |
A malicious SSH server can write arbitrary files on the asyncssh SCP client's filesystem by sending filenames containing ../ traversal sequences. The SCP receive path does not currently sanitize server-provided filenames. By chaining directory traversals via the D (directory) action, an attacker can escape any target directory and overwrite ~/.bashrc, ~/.ssh/rc, or ~/.ssh/authorized_keys, achieving code execution. This is the same vulnerability class as CVE-2019-6111. The mitigation applied in OpenSSH does not appear to have been adopted in asyncssh.
Steps to exploit:
Step 1 - Normal usage: Application calls await asyncssh.scp((conn, 'file'), '/home/user/downloads/'). This is the standard, documented API.
Step 2 - SCP protocol: asyncssh opens an SSH exec channel, runs scp -f file. The server controls the filename field:
C0644 100 ../pwned.txt\n (simple traversal)
D0755 0 ..\n (traverse up, repeat as needed)
C0644 47 .bashrc\n (write payload)
E\nStep 3 - _parse_cd_args (scp.py:134-142) returns the filename verbatim:
def _parse_cd_args(args: bytes) -> Tuple[int, int, bytes]:
permissions, size, name = args.split(None, 2)
return int(permissions, 8), int(size), name # no sanitizationThe returned name is not passed through basename() and is not checked for .. or / components.
Step 4 - _recv_files (scp.py:706-713) joins the unsanitized name:
new_dstpath = posixpath.join(dstpath, name)With dstpath=b'/home/user/downloads/subdir' and name=b'../pwned.txt', this resolves to /home/user/downloads/pwned.txt, outside the target.
Step 5 - File write: _recv_file opens the traversed path via self._fs.open(dstpath, 'wb') and writes attacker-controlled content. The resolved path is not checked against the target directory boundary.
Step 6 - RCE chains:
| Target | Execution trigger | Reliability |
|---|---|---|
~/.bashrc |
Next terminal open | High |
~/.profile |
Next login | High |
~/.ssh/rc |
Next SSH connection (requires sshd) | High |
~/.ssh/authorized_keys |
Attacker logs in with command= |
Medium |
Reproduction:
Link to reproduction script: path_traversal_poc.zip
docker build -t asyncssh-scp-traversal -f Dockerfile .
docker run --rm asyncssh-scp-traversalThe attached poc_scp_traversal.py starts a malicious SSH server in-process using asyncssh's own API, then downloads from it via asyncssh.scp().
Expected Output:
<img width="1400" height="815" alt="image" src="https://github.com/user-attachments/assets/496745e4-d11d-4ed8-bddd-d15dd13d1751" />Czego dotyczy
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| Platforma | Paczka | Podatne wersje | Poprawka w wersji |
|---|---|---|---|
| Python (PyPI) | asyncssh | < 2.23.1 | 2.23.1 |
Odnośniki
- https://github.com/ronf/asyncssh/security/advisories/GHSA-2wxc-x7rj-hg8f
- https://nvd.nist.gov/vuln/detail/CVE-2026-54591
- https://github.com/ronf/asyncssh/commit/d730803b8e4e94c20c7580d90f94d1e05f9f58de
- https://github.com/ronf/asyncssh
- https://github.com/ronf/asyncssh/releases/tag/v2.23.1
- https://pypi.org/project/asyncssh
- https://github.com/advisories/GHSA-2wxc-x7rj-hg8f
- Wektor CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H- Słabość (CWE)
CWE-22- Platforma
- Python (PyPI)
- Paczka
asyncssh- Ujawniono
- 26.08.2026
- Aktualizacja
- 11.10.2026 15:18
Źródła i licencje
OSV / GitHub Advisory Database - PYSEC-2026-3808 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-2wxc-x7rj-hg8f - CC BY 4.0
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