CVE-2026-23942: SFTP root escape via component-agnostic prefix check in ssh_sftpd

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-13 · updated 2026-07-24
Weakness: CWE-22

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 before OTP 28.4.1, OTP 27.3.4.9 and OTP 26.2.5.18, corresponding to ssh from 3.0.1 before 5.5.1, 5.2.11.6 and 5.1.4.14.

Affected products

Erlang OTP: from 17.0 before 26.2.5.18; from 27.0 before 27.3.4.9; from 28.0 before 28.4.1 — fixed in 26.2.5.18, 27.3.4.9, 28.4.1
Erlang/Ssh: from 3.0.1 before 5.1.4.14; from 5.2 before 5.2.11.6; from 5.5 through 5.5.1 — fixed in 5.1.4.14, 5.2.11.6

How to fix

Upgrade to a fixed version: Erlang OTP 26.2.5.18, 27.3.4.9, 28.4.1; Erlang/Ssh 5.1.4.14, 5.2.11.6. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-23942 or the next vulnerability affects your stack