Weakness Type (CWE)

CWE-204 — CWE-204 Observable Response Discrepancy

CAPEC

CVSS 4.0 Score

2.3

LOW

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Vulnerability description

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.

Affected

pkg:otp/ssh

Module Source File Routine
ssh_sftpd src/ssh_sftpd.erl ssh_sftpd:handle_op/4
Status Type Version Changes / Fixed in
affected otp ⓘ 3.0.1
  • unaffected at 6.0.2
  • unaffected at 5.5.2.2
  • unaffected at 5.2.11.9

pkg:github/erlang/otp

Module Source File Routine
ssh_sftpd lib/ssh/src/ssh_sftpd.erl ssh_sftpd:handle_op/4
Status Type Version Changes / Fixed in
affected otp ⓘ 17.0
affected git ⓘ 84adefa331

Configurations

The SFTP subsystem must be configured with the root option in ssh_sftpd:subsystem_spec/1, and the operator must rely on it to provide filesystem path isolation. The root option is not set by default.

Workarounds

  • Use OS-level chroot to run the Erlang VM or SFTP server process in an isolated filesystem environment, eliminating reliance on the application-level root option.
  • Ensure the SFTP server port on the machine running the Erlang/OTP SFTP server is not reachable from untrusted machines.
  • Ensure that no sensitive information (usernames, project names, mount topology) is inferrable from the existence or non-existence of paths on the host filesystem.

References

Credits

  • Finder: Mohamed Ali IBNAL HAJALI / Ericsson
  • Remediation developer: Michał Wąsowski
  • Remediation reviewer: Jakub Witczak

CVE record as JSON:  GET /cves/CVE-2026-53422.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-53422.json