Linux systems affected by ‘GHOST’ vulnerability

Proof-of-concept email gives remote access to Exim mail server.

If you administer

Linux

-based systems, you’d better schedule some time for patching, as a serious buffer overflow vulnerability has been discovered in the

glibc

library.

The vulnerability exists in the gethostbyname() and gethostbyname2() functions, which are used to resolve hostnames – hence any piece of software that connects to the Internet is potentially vulnerable.

The good news is that these functions

shouldn’t be used

anyway and, in fact, were fixed in May 2013. The bad news is that not only do many programs still use them, but that, when the fix was applied, it wasn’t recognised as a security threat – hence many stable and long-term-support distributions remained vulnerable.

The vulnerability was

discovered

by researchers from

Qualys

, who gave it the name ‘GHOST’ (its more official name is

CVE-2015-0235

) and also designed a fitting logo. In the

detailed advisory

, the researchers explain how they wrote a proof-of-concept exploit where an attacker gains full control of an

Exim

mail server merely by sending specially crafted strings during the SMTP transaction.

GHOST is reminiscent of the ‘Shellshock’ vulnerability in

bash

that was discovered last year. Although less trivial to exploit, it could potentially affect any piece of software. The good news is that

Qualys


believes

many other widely used software packages that call the affected functions, including

Apache

,

nginx

,

openssh

,

Sendmail

and

Postfix

, are not vulnerable as the buffer overflow cannot be triggered.

Still, even if you don’t run

Exim

, there is no good reason not to patch; most

Linux

distributions have made patches available.

And of course, there is always the possibility that someone already knew about GHOST and had secretly been exploiting it all this time.

Update:

this blog post previously stated that the exploit against

Exim

worked by sending an email. This is

incorrect

.

Posted on 28 January 2015 by

Martijn Grooten