GHSA-246w-jgmq-88fg is a critical-severity (CVSS 10) vulnerability in github.com/jkroepke/openvpn-auth-oauth2. O3 Security confirms whether GHSA-246w-jgmq-88fg is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access
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 | 1.27.3 |
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. 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/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 pinpoints whether GHSA-246w-jgmq-88fg 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-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 detects GHSA-246w-jgmq-88fg across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.