CVE-2026-41070

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access

10.0 CriticalFix available

openvpn-auth-oauth2 is a plugin/management interface client for OpenVPN server to handle an OIDC based single sign-on (SSO) auth flows. From version 1.26.3 to before version 1.27.3, 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. This issue has been patched in version 1.27.3.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: None

Exploit likelihood

0.44%Up 0.4 points since May 9, 2026

What each source reports

CVE List Score used 10.0

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access

Record: CVE-2026-41070
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

EUVDEUVD-2026-28789 10.0

Record: EUVD-2026-28789
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-246w-jgmq-88fg 10.0

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access

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.

Fix commit: 36f69a6
Fix PR: #829

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.

Record: GHSA-246w-jgmq-88fg
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

NVD 10.0

Record: CVE-2026-41070
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

OSV 10.0

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access

Record: CVE-2026-41070
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

OSVDEBIAN-CVE-2026-41070 10.0

Record: DEBIAN-CVE-2026-41070
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Updated: 2026-11-02

Show 4 moreShow less

OSVGHSA-246w-jgmq-88fg 10.0

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access

Summary

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.

Root Cause

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.

Fix commit: 36f69a6
Fix PR: #829

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.

Record: GHSA-246w-jgmq-88fg
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

OSVUBUNTU-CVE-2026-41070 10.0

Record: UBUNTU-CVE-2026-41070
CVSS 3.1: 10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Updated: 2026-11-02

OSVGO-2026-4963 No score

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access in github.com/jkroepke/openvpn-auth-oauth2

openvpn-auth-oauth2 returns FUNC_SUCCESS on client-deny, allowing unauthenticated VPN access in github.com/jkroepke/openvpn-auth-oauth2

Record: GO-2026-4963
Updated: 2026-11-02

OSVopenSUSE-SU-2026:21483-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
GO-2026-5933 GHSA-3g4q-2f67-2gvh
GO-2026-5934 GHSA-59qp-cfj3-rp64
GO-2026-5935 GHSA-7856-g3gv-9wq8
GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
GO-2026-5942 CVE-2026-46600
GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
GO-2026-5969 GHSA-g936-7jqj-mwv8
GO-2026-5970 CVE-2026-56852
GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
GO-2026-5981 GHSA-mqxv-9rm6-w8qc
GO-2026-5982 GHSA-pqg7-v6wh-3pfp
GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
GO-2026-5985 GHSA-7rx3-5wx3-5v76
GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…

Record: openSUSE-SU-2026:21483-1
Updated: 2026-11-02

Affected products

jkroepke openvpn-auth-oauth2

Affected packages

Affected packages
Package	Affected	Fixed
`github.com/jkroepke/openvpn-auth-oauth2` Go	1.26.3 up to 1.27.3	1.27.3
`openvpn-auth-oauth2` Debian:14	before 1.27.3-1, plus listed versions 1.26.2+dfsg-11.26.4+dfsg-11.26.4+dfsg-21.26.4+dfsg-31.26.4+dfsg-4 Show 6 moreShow less 1.26.4+dfsg-51.26.4+dfsg-61.27.0-11.27.0-21.27.1-11.27.2-1	1.27.3-1
`openvpn-auth-oauth2` Ubuntu:26.10	All versions, plus listed versions 1.27.0-21.28.0-11.28.3-2	None known
`openvpn-auth-oauth2` Ubuntu:Pro:26.04:LTS	All versions, plus listed versions 1.27.0-21.27.0-2ubuntu0.1~esm1	None known
`govulncheck-vulndb` openSUSE:Leap 16.0 From an advisory covering 1734 CVEs	before 0.0.20260723T184607-160000.1.1	0.0.20260723T184607-160000.1.1

History

History
Recorded	Changed	Sources
Nov 6, 2026	affected, facts
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-41070 is a critical vulnerability (CVSS 10.0) in Jkroepke Openvpn-auth-oauth2, published April 22, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.44%, the 38th percentile. Fixed in github.com/jkroepke/openvpn-auth-oauth2 1.27.3.

References

Show 194 moreShow less

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Left out here: 1,547 references and the rest of 1 source description. The JSON record has them.