Trivial Authentication Bypass In Libssh Leaves Servers Wide Open

Ars Technica reports of 'a four-year-old bug in the Secure Shell implementation known as libssh that makes it trivial for just about anyone to gain unfettered administrative control of a vulnerable server.' It's not clear how many sites or devices may be vulnerable since neither the widely used OpenSSH nor Github's implementation of libssh was affected. From the report: The vulnerability, which was introduced in libssh version 0.6 released in 2014, makes it possible to log in by presenting a server with a SSH2_MSG_USERAUTH_SUCCESS message rather than the SSH2_MSG_USERAUTH_REQUEST message the server was expecting, according to an advisory published Tuesday. Exploits are the hacking equivalent of a Jedi mind trick, in which an adversary uses the Force to influence or confuse weaker-minded opponents. The last time the world saw an authentication-bypass bug with such serious consequences and requiring so little effort was 11 months ago, when Apple's macOS let people log in as admin without entering a password.

On the brighter side, there were no immediate signs of any big-name sites being bitten by the bug, which is indexed as CVE-2018-10933. While Github uses libssh, the site officials said on Twitter that 'GitHub.com and GitHub Enterprise are unaffected by CVE-2018-10933 due to how we use the library.' In a follow-up tweet, GitHub security officials said they use a customized version of libssh that implements an authentication mechanism separate from the one provided by the library. Out of an abundance of caution, GitHub has installed a patch released with Tuesday's advisory. Another limitation: only vulnerable versions of libssh running in server mode are vulnerable, while the client mode is unaffected. Peter Winter-Smith, a researcher at security firm NCC who discovered the bug and privately reported it to libssh developers, told Ars the vulnerability is the result of libssh using the same machine state to authenticate clients and servers. Because exploits involve behavior that's safe in the client but unsafe in the server context, only servers are affected.

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