CVE-2026-40876 SFTP root escape via prefix-based path validation in goshs

What is CVE-2026-40876?

CVE-2026-40876 is a high-severity path traversal vulnerability in patrickhener goshs, published on 21 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

goshs is a SimpleHTTPServer written in Go. Prior to 2.0.0-beta.6, goshs contains an SFTP root escape caused by prefix-based path validation. An authenticated SFTP user can read from and write to filesystem paths outside the configured SFTP root, which breaks the intended jail boundary and can expose or modify unrelated server files. The SFTP subsystem routes requests through sftpserver/sftpserver.go into DefaultHandler.GetHandler() in sftpserver/handler.go, which forwards file operations into readFile, writeFile, listFile, and cmdFile. All of those sinks rely on sanitizePath() in sftpserver/helper.go. helper.go uses a raw string-prefix comparison, not a directory-boundary check. Because of that, if the configured root is /tmp/goshsroot, then a sibling path such as /tmp/goshsroot_evil/secret.txt incorrectly passes validation since it starts with the same byte prefix. This vulnerability is fixed in 2.0.0-beta.6.

Weakness: CWE-22

Which versions are affected by CVE-2026-40876?

6 open source packages ship an affected version, including github.com/patrickhener/goshs and github.com/patrickhener/goshs/v2. It affects 1 product.

Products include Goshs Goshs.

How do I fix CVE-2026-40876?

Upgrade to a fixed version.

Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.

Is CVE-2026-40876 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40876 exists.

Other vulnerabilities in patrickhener goshs

• CVE-2026-40884 goshs: Empty-username SFTP password authentication bypass in goshs Critical 9.8
• CVE-2026-35392 goshs has an Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in goshs PUT Upload Critical 9.8
• CVE-2026-35393 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in goshs POST multipart upload Critical 9.8
• CVE-2026-35471 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in goshs Critical 9.8
• CVE-2026-40189 goshs has a file-based ACL authorization bypass in goshs state-changing routes Critical 9.3

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-5h6h-7rc9-3824, GO-2026-5146.