SFTPServer.map_path() removes a single leading slash from a client‑supplied path, then normalises the path and joins it with the server’s chroot directory. If the user supplies a path that begins with exactly two slashes, normalisation preserves the double‑leading‑slash pattern, and the later join treats the remaining pathname as absolute, bypassing the chroot. This allows an authenticated SFTP user to read or write files anywhere on the host filesystem with the permissions of the server process, which may enable arbitrary code execution when writable targets are reachable.

The vulnerability affects the AsyncSSH Python library provided by ronf, specifically any installation using Version 2.24.0 or earlier. The issue was resolved in release 2.24.1.

The CVSS score of 8.8 classifies this flaw as a high‑severity problem. EPSS data is not available, and the vulnerability is not listed in the CISA KEV catalog. The likely attack vector involves an authenticated SFTP client; once authenticated, an attacker can supply a specially crafted path to escape the intended chroot and access arbitrary files. Because the exploit requires a valid SFTP session, the immediate risk is high for servers that expose SFTP to untrusted users or run with elevated privileges. Proper remediation is therefore urgent.