Critical Linux Kernel Flaw Gives Root Access to Attackers

Multiple Linux distributions including all current versions of Red Hat Enterprise Linux and CentOS contain a newly discovered bug that gives attackers a way to obtain full root access on vulnerable systems.

The integer overflow flaw (CVE-2018-14634)exists in a critical Linux kernel function for memory management and allows attackers with unprivileged local access to a system to escalate their privileges. Researchers from security vendor Qualys discovered the issue and have developed a proof of concept exploit.

A patch for the flaw, which Qualys has dubbed "Mutagen Astronomy," is available, and most Linux distributions have already "backported" the patch for older versions of their kernels. But Red Hat Linux Enterprise, CentOS, and the Debian 8, or the "oldstable" version, are yet not patched, Qualys said in a security advisory this week.

In a statement, Red Hat said the issue impacts Red Hat Enterprise Linux 6, 7, and Red Hat Enterprise MRG 2. But versions of the Linux kernel shipped with Red Hat Linux 5 are not impacted, and systems with less than 32GB of memory are also very unlikely to be impacted by the vulnerability, "as they do not have a large enough address space to exploit this flaw," Red Hat said.

The vulnerability has been assigned a CVSS base score of 7.8, but Red Hat has assessed it as having high impact on confidentiality, integrity, and availability.  The vendor described the vulnerability as being exploitable with no user-interaction needed and involving low attack complexity.

Anagram

Jimmy Graham, director of product management and vulnerability management at Qualys, says the name "Mutagen Astronomy" is an anagram of "Too Many Arguments," which is the fundamental vulnerability being exploited.

The flaw is another reminder of the importance of the need for layered defenses, he says. Often attackers who exploit a remote vulnerability—such as a Web-application exploit, for instance—only gain unprivileged access on the vulnerable system.

So cybercriminals typically combine the use of lower-severity flaws with more severe ones like the Mutagen Astronomy flaw to create a very functional attack, Graham explains. "This type of vulnerability is often used in conjunction with other kinds of attacks," he says. "If an attacker has an existing foothold on a system but is unable to escalate to root, they may utilize a vulnerability like this to fully compromise the system."

That is why proper vulnerability and patch management is crucial, and should not be limited only to remediation of "critical" vulnerabilities, he adds.

Linux developer Kees Cook developed the patch for the flaw based on previous work by grsecurity, and most Linux distrbutions have backported it to their long-term-supported kernels. A backported patch is a patch that has been developed for the current mainline Linux kernel but can be applied to older, or long-term-supported (LTS) kernels, Graham says.

It's up to each Linux provider to decide if a patch is important enough for them to backport, and whether there's a likelihood of the patch harming the stability of their older LTS kernels.

"In this particular case, most distributions backported this patch, but Red Hat Enterprise Linux and CentOS did not," Graham says. All versions of these distributions are affected - even in their default and minimal installations, he notes.

Red Hat's advisory includes advice on how organizations can mitigate the vulnerability. The company will address the issue in updates for Red Hat Enterprise Linux 6, 7, and other affected versions.

Related Content:

Black Hat Europe returns to London Dec 3-6 2018  with hands-on technical Trainings, cutting-edge Briefings, Arsenal open-source tool demonstrations, top-tier security solutions and service providers in the Business Hall. Click for information on the conference and to register.