Another dangerous vulnerability has been discovered in Linux kernel that dates back to 2009 and affects a large number of Linux distros, including Red Hat, Debian, Fedora, OpenSUSE, and Ubuntu.

The latest Linux kernel flaw (CVE-2017-2636), which existed in the Linux kernel for the past seven years, allows a local unprivileged user to gain root privileges on affected systems or cause a denial of service (system crash).

Positive Technologies researcher Alexander Popov discovered a race condition issue in the N_HLDC Linux kernel driver – which is responsible for dealing with High-Level Data Link Control (HDLC) data – that leads to double-free vulnerability.

"Double Free" is one of the most common memory corruption bug that occurs when the application releases same memory location twice by calling the free() function on the same allocated memory.

An unauthenticated attacker may leverage this vulnerability to inject and execute arbitrary code in the security context of currently logged in user.

The vulnerability affects the majority of popular Linux distributions including Red Hat Enterprise Linux 6, 7, Fedora, SUSE, Debian, and Ubuntu.

Since the flaw dates back to June 2009, Linux enterprise servers and devices have been vulnerable for a long time, but according to Positive Technologies, it is hard to say whether this vulnerability has actively been exploited in the wild or not.
"The vulnerability is old, so it is widespread across Linux workstations and servers," says Popov. "To automatically load the flawed module, an attacker needs only unprivileged user rights. Additionally, the exploit doesn't require any special hardware."
The researcher detected the vulnerability during system calls testing with the syzkaller fuzzer, which is a security code auditing software developed by Google.

Popov then reported the flaw to on February 28, 2017, along with the exploit prototype, as well as provided the patch to fix the issue.

The vulnerability has already been patched in the Linux kernel, and the security updates along with the vulnerability details were published on March 7.

So, users are encouraged to install the latest security updates as soon as possible, but if unable to apply the patch, the researcher advised blocking the flawed module (n_hdlc) manually to safeguard enterprise as well as home use of the operating system.

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