Security Experts:

Privilege Escalation Vulnerability Found in Linux Kernel

A researcher has identified a serious vulnerability in the Linux kernel that can be exploited by a local attacker to escalate privileges on affected systems.

The issue, discovered by AMA Capital Management co-founder Andrew Lutomirski, is related to CVE-2014-9090, a Linux kernel denial-of-service (DoS) vulnerability reported recently by Lutomirski.

CVE-2014-9090 is caused by the improper handling of faults associated with the Stack Segment (SS) register on the x86 architecture. Lutomirski discovered the new kernel vulnerability, CVE-2014-9322, after Borislav Petkov asked some questions about CVE-2014-9090.

"Any kernel that is not patched against CVE-2014-9090 is vulnerable to privilege escalation due to incorrect handling of a #SS fault caused by an IRET instruction. In particular, if IRET executes on a writeable kernel stack (this was always the case before 3.16 and is sometimes the case on 3.16 and newer), the assembly function general_protection will execute with the user's gsbase and the kernel's gsbase swapped," Lutomirski explained in an advisory.

"This is likely to be easy to exploit for privilege escalation, except on systems with SMAP or UDEREF. On those systems, assuming that the mitigation works correctly, the impact of this bug may be limited to massive memory corruption and an eventual crash or reboot," he added.

A CVSS v2 base score of 7.2 has been assigned to this Linux kernel privilege escalation vulnerability. The fix for CVE-2014-9090 also patches CVE-2014-9322, Lutomirski said.

Red Hat, which rates the bug as "important," released kernel package updates that address the flaw on Thursday. Red Hat Enterprise Linux 4, 5, 6, and 7, and Red Hat Enterprise MRG 2 are affected.

Several Linux-related security bugs have been discovered over the past weeks. A few days ago, researchers at Alert Logic reported identifying what appears to be a different Linux privilege escalation vulnerability. The flaw, dubbed "Grinch," is actually a common configuration issue related to Polkit.

Red Hat dismissed the reports, arguing that what the security firm described is expected behavior. Red Hat says "Grinch" is neither a security issue nor a bug.

A different vulnerability, which affects several Linux distributions, has been found in the mailx utility. The flaw has been confirmed and the developers of many Unix-like operating systems have already released patches for it.

Related: Exploring the Misconceptions of Linux Security

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.