CVE-2026-23942
SFTP root escape via component-agnostic prefix check in ssh_sftpd
Weakness Type (CWE)
CWE-22 — CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
CAPEC
Vulnerability description
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') vulnerability in Erlang OTP (ssh_sftpd module) allows Path Traversal.This vulnerability is associated with program files lib/ssh/src/ssh_sftpd.erl and program routines ssh_sftpd:is_within_root/2.
The SFTP server uses string prefix matching via lists:prefix/2 rather than proper path component validation when checking if a path is within the configured root directory. This allows authenticated users to access sibling directories that share a common name prefix with the configured root directory. For example, if root is set to /home/user1, paths like /home/user10 or /home/user1_backup would incorrectly be considered within the root.
This issue affects OTP from OTP 17.0 until OTP 28.4.1, OTP 27.3.4.9 and OTP 26.2.5.18, corresponding to ssh from 3.0.1 until 5.5.1, 5.2.11.6 and 5.1.4.14.
Affected
pkg:otp/ssh
| Module | Source File | Routine |
|---|---|---|
ssh_sftpd
|
src/ssh_sftpd.erl
|
ssh_sftpd:is_within_root/2
|
| Status | Type | Version | Changes / Fixed in |
|---|---|---|---|
| affected | otp ⓘ | 3.0.1
|
|
pkg:github/erlang/otp
| Module | Source File | Routine |
|---|---|---|
ssh_sftpd
|
lib/ssh/src/ssh_sftpd.erl
|
ssh_sftpd:is_within_root/2
|
| Status | Type | Version | Changes / Fixed in |
|---|---|---|---|
| affected | otp ⓘ | 17.0
|
|
| affected | git ⓘ | initial
|
|
Workarounds
- Use OS-level chroot to run the Erlang VM/SFTP server process in an isolated filesystem environment.
- Ensure that no sensitive or precious data is readable or writable by the OS user running the Erlang VM.
- Ensure that the SFTP server port is not reachable from untrusted machines.
- Use directory naming conventions that avoid common prefixes (e.g., /home/users/alice/ instead of /home/user1/).
References
- https://github.com/erlang/otp/security/advisories/GHSA-4749-w85x-hw9h vendor-advisory
- https://github.com/erlang/otp/commit/27688a824f753d4c16371dc70e88753fb410590b patch
- https://github.com/erlang/otp/commit/9e0ac85d3485e7898e0da88a14be0ee2310a3b28 patch
- https://github.com/erlang/otp/commit/5ed603a1211b83b8be2d1fc06d3f3bf30c3c9759 patch
Credits
- Reporter: Luigino Camastra / Aisle Research
- Remediation developer: Jakub Witczak
- Remediation reviewer: Michał Wąsowski
CVE record as JSON:
GET /cves/CVE-2026-23942.json
OSV record as JSON:
GET /osv/EEF-CVE-2026-23942.json