GHSA-246w-jgmq-88fg is a critical-severity (CVSS 10) Improper Authentication vulnerability in github.com/jkroepke/openvpn-auth-oauth2. A fix is available for github.com/jkroepke/openvpn-auth-oauth2 — see the affected versions and patch details below.
openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-246w-jgmq-88fg.
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-246w-jgmq-88fg 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 378,156 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/jkroepke/openvpn-auth-oauth2Real-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
When openvpn-auth-oauth2 is deployed in the experimental plugin mode (shared library loaded by OpenVPN via the plugin directive), clients that do not support WebAuth/SSO (e.g., the openvpn CLI on Linux) are incorrectly admitted to the VPN despite being denied by the authentication logic. The default management-interface mode is not affected because it does not use the OpenVPN plugin return-code mechanism.
Impact
Authentication bypass — any VPN client that does not advertise WebAuth/SSO support (IV_SSO=webauth) is granted full network access without completing OIDC authentication.
This affects only deployments running the experimental plugin mode in versions 1.26.3 through 1.27.2. The default and recommended deployment via the management interface is not affected.
An unauthenticated attacker can connect to the OpenVPN server using any standard OpenVPN client that does not support webauth (e.g., the Linux openvpn CLI). The plugin correctly issues a client-deny command via the management interface, but returns OPENVPN_PLUGIN_FUNC_SUCCESS (status=0) to OpenVPN. Because the auth_control_file content is only consulted when the plugin returns FUNC_DEFERRED, OpenVPN interprets status=0 as "authentication passed" and admits the client — granting full access to the internal network behind the VPN.
Root Cause
In lib/openvpn-auth-oauth2/openvpn/handle.go, the ClientAuthDeny branch of handleAuthUserPassVerify wrote "0" (deny) to the auth_control_file but returned OPENVPN_PLUGIN_FUNC_SUCCESS. OpenVPN only reads the auth_control_file when the plugin returns FUNC_DEFERRED; a synchronous FUNC_SUCCESS return is treated as immediate approval regardless of file contents.
Before fix:
case management.ClientAuthDeny:
// ... writes "0" to auth_control_file ...
if err := openVPNClient.WriteToAuthFile("0"); err != nil {
// only returned ERROR on write failure
return c.OpenVPNPluginFuncError
}
return c.OpenVPNPluginFuncSuccess // ← BUG: OpenVPN sees this as "auth passed"
After fix (commit 36f69a6):
case management.ClientAuthDeny:
// ... writes "0" to auth_control_file ...
if err := openVPNClient.WriteToAuthFile("0"); err != nil {
logger.ErrorContext(p.ctx, "write to auth file", slog.Any("err", err))
}
return c.OpenVPNPluginFuncError // ← FIX: OpenVPN now correctly rejects the client
Patches
This vulnerability is fixed in v1.27.3. Users of the experimental plugin mode should upgrade immediately.
Workarounds
- Switch to standalone management client mode (the default, non-plugin deployment). This mode is not affected by the vulnerability because authentication decisions are communicated entirely through the management interface protocol, not through the plugin return code.
- Restrict VPN access at the network level to only clients known to support WebAuth/SSO (e.g., OpenVPN Connect 3+), although this is difficult to enforce reliably and is not recommended as a sole mitigation.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/jkroepke/openvpn-auth-oauth2 | ≥ 1.26.3&&< 1.27.3 | 1.27.3go get github.com/jkroepke/openvpn-auth-oauth2@v1.27.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/jkroepke/openvpn-auth-oauth2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/jkroepke/openvpn-auth-oauth2 to 1.27.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-246w-jgmq-88fg 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-246w-jgmq-88fg can be triaged on real exposure rather than presence alone.
Tailored to GHSA-246w-jgmq-88fg. 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-246w-jgmq-88fg in your dependencies?
O3 Security finds GHSA-246w-jgmq-88fg across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.