CVE-2020-15078

Overview

OpenVPN 2.5.1 and earlier versions allow remote attackers to bypass authentication and access control channel data on servers configured with deferred authentication, which can be used to potentially trigger further information leaks.

Detailed Description

This bug permits - under very specific circumstances - tricking a server using delayed authentication (either via a plugin or management) into returning a PUSH_REPLY before the AUTH_FAILED message, which can possibly be used to gather information about a VPN setup.

In conjunction with "--auth-gen-token" or a user-specific token auth solution, it may be possible to access a VPN with an otherwise-invalid account.

Fixed OpenVPN Versions

This vulnerability has been addressed in the following releases:

• release/2.5
  • Commit f7b3bf067ffce72e7de49a4174fd17a3a83f0573
  • Commit 3d18e308c4e7e6f7ab7c2826c70d2d07b031c18a
  • Commit 3aca477a1b58714754fea3a26d0892fffc51db6b
• release/2.4
  • Commit 0e5516a9d656ce86f7fb370c824344ea1760c255

The following releases include the fix:

• OpenVPN 2.5.2
• OpenVPN 2.4.11

Recommendations

If you are not using auth-gen-token, a plugin, or management in your configuration, your setup should be safe. However, if in doubt, consider upgrading. If you know you're using deferred-auth, it is recommended to upgrade.