Affected: Homebrew: dvc

| | | |---|---| | 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.

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**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:

```python 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 thro…

Affected: ronf asyncssh

AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Prior to 2.23.1, a malicious SSH server can write arbitrary files on the asyncssh SCP client's filesystem by sending filenames containing ../ traversal sequences because _parse_cd_args in scp.py returns server-provided names verbatim and _recv_files joins them to the destination path without enforcing the target directory boundary. This issue is fixed in version 2.23.1.

Affected: PyPI: 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:

```python 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 thro…