CVE-2026-53422
LowCVSS 2.3Exploitation Probability (EPSS)
Low risk25th percentile — higher than 25% of all known CVEs
Summary
An Observable Response Discrepancy vulnerability in the ssh_sftpd module of Erlang OTP SSH allows an authenticated SFTP user to enumerate the existence of files and directories outside the configured root directory. The SSH_FXP_REALPATH handler does not canonicalize the path before checking restrictions, enabling the use of '..' components to bypass validation and obtain information about the existence of paths on the filesystem.
Risk Assessment
The risk is information disclosure about the filesystem structure, including the existence of sensitive files, directories, and mount points, which may assist further attacks when combined with other vulnerabilities. No file contents, credentials, or write access are directly exposed.
Recommendation
Immediately upgrade Erlang OTP to version 29.0.3, 28.5.0.3, or 27.3.4.14 (or later) depending on the branch in use. If an upgrade is not possible, restrict trust for authenticated SFTP users and monitor for unusual REALPATH requests.
Original NVD description (English source)
Observable Response Discrepancy vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to enumerate the existence of files and directories outside the configured root directory. The SSH_FXP_REALPATH handler in ssh_sftpd calls relate_file_name/3 with Canonicalize=false, unlike every other SFTP operation handler. This allows .. components in the requested path to bypass the is_within_root/2 check without being resolved. The un-canonicalized path then enters resolve_symlinks/2, which walks up the directory tree above the configured root and issues read_link() syscalls on arbitrary filesystem paths. An authenticated SFTP client can exploit this by sending a REALPATH request with a crafted traversal path. The server response differs depending on whether the target path exists on the host filesystem (SSH_FXP_NAME when the path resolves successfully, SSH_FX_NO_SUCH_FILE when it does not). This creates a path-existence oracle that an attacker can use to enumerate the filesystem structure outside the configured root, including the existence of sensitive files, directories, and mount points. The vulnerability leaks only the existence of paths. No file contents, credentials, or write access are obtainable through this issue alone. The information gained may assist further attacks when combined with other vulnerabilities. This vulnerability is associated with program files lib/ssh/src/ssh_sftpd.erl and program routine ssh_sftpd:handle_op/4. This issue affects OTP from OTP 17.0 until OTP 29.0.3, 28.5.0.3, and 27.3.4.14 corresponding to ssh from 3.0.1 until 6.0.2, 5.5.2.2, and 5.2.11.9.