Know every vulnerabilitybefore it knows you.
DevGuard continuously monitors your dependencies and alerts you when CVEs like this one affect your stack — with real-time threat intelligence built for developers.
GHSA-2wxc-x7rj-hg8f
asyncssh| | | |---|---| | 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\n
Step 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 sanitization
The 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-traversal
The 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" />Upload your own SBOM in CycloneDX 1.6 or higher (JSON) directly here to check your vulnerabilities.
Drag and drop some file here, or click to select
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
Browse More
Continuously monitor your dependencies and get alerted when vulnerabilities like this one affect your stack.
Checkout DevGuard