GHOST bug is real and possibly nasty, but not so spooky

Several security experts say GHOST, the latest far-reaching open source security bug, is a potentially serious threat and will be annoying to fix, but is probably not catastrophic.

A day after GHOST was revealed, the consensus among several security experts is that the risk to affected systems is on the low-side and, for now, it is less of a risk than previously disclosed open source bugs like Shellshock and Heartbleed.

GHOST is a bug in older versions of GNU C Library, a core component of Linux, that left several major distributions exposed to a remotely exploitable buffer overflow flaw that can be triggered by GetHost functions in the library.

It was serious enough for maintainers of Debian, Red Hat Enterprise Linux, CentOS and Ubuntu to create patches to remedy the issue in affected versions. In addition, a proof of concept exploit against the Exim mail server for Unix systems could also bypass anti-exploitation measures of the OS.

These details remain true, however security experts who’ve reviewed what’s known about GHOST say the bug is difficult to exploit.

For one, the number of potential avenues to attack vulnerable applications are limited and currently there are no known ways to attack the bug over the web, which, Pawan Kinger, director of Trend Micro's Deep Security Labs, points out, reduces the risk significantly.

“Exploitation is very difficult as an attacker only has a small amount of initial exploit code that can be used: 4 or 8 bytes (depending on whether the system is a 32- or 64-bit system). Additional code must be written to an address referenced by a pointer which the attacker can modify. As a result, many apps are not at risk. So far, we are not aware of any potential web attack vectors, which reduces the attack surface considerably,” Kinger noted.

Some of those that aren’t at risk were outlined by Qualys as potential targets that it couldn’t trigger the buffer overflow in.

Robert Graham, a researcher from Errata Security, said that since only a few bytes can be overwritten, chances are that hackers can only crash a program and not gain code execution — the latter allowing an attacker to take full control of a machine.

The threat to un-patched systems however could change over time and the real risk may lie in the fact that GHOST will be difficult to eradicate. The longer the bug remains unfixed on systems, the higher the chances are that hackers will have developed attacks for it. That, according to Graham, means that hackers are more likely to be able to exploit previously disclosed bugs like Shellshock and Heartbleed than Ghost.

Even if the threat is not particularly serious today, the general advice is that affected systems should be updated. And as penetration testing firm Rapid7 and independent researchers have pointed out, admins of affected systems will need to reboot affected systems after applying the fix or else they may remain vulnerable.

This article is brought to you by Enex TestLab, content directors for CSO Australia.

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