Tag Archives: OpenVPN

OpenVPN Vulnerable To Shellshock Exploit

There’s a whole list of Shellshock PoCs here on Github including the one for OpenVPN – Shellshocker PoCs. The exploit walkthrough is available here, including the OpenVPN config and log output – OpenVPN ShellShock PoC.

The Shellshock Bash bug, the gift that just keeps on taking, could also sting OpenVPN users, according to researcher Fredrick Stromberg. Pre-authentication vectors affect communication through the popular and formerly secure VPN platform, he says.

Shellshock affected the crucial and ubiquitous *nix component Bash up to and including version 4.3. Mullvad chief technology officer Stromberg described the flaw in a forum post overnight, adding that he disclosed the vulnerability to OpenVPN sometime last week.

“OpenVPN servers are vulnerable to Shellshock under certain configurations,” Stromberg said. “OpenVPN has a number of configuration options that can call custom commands during different stages of the tunnel session. Many of these commands are called with environmental variables set, some of which can be controlled by the client.

“One option used for username+password authentication is auth-user-pass-verify. If the called script uses a vulnerable shell, the client simply delivers the exploit and payload by setting the username. This attack vector is pre-auth.”

A proof of concept for the exploit has surfaced online. Those using OpenVPN can dodge Shellshock by preventing Bash from running scripts. OpenVPN’s Gert Doering told Threat Post OpenVPN was vulnerable only on systems where /bin/sh points to /bin/bash, or when scripts running bash as an interpreter were called explicitly.

 

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