A vulnerability in the Linux kernel, initially identified two years ago, has recently been reclassified as a potential local privilege escalation flaw. Known as CVE-2017-1000253, the issue was first discovered by Google researcher Michael Davidson in April 2015, but at the time, it did not raise security concerns significant enough to warrant immediate action.
This vulnerability affects a wide range of major Linux distributions, including Red Hat, Debian, and CentOS. Research from Qualys Labs indicates that it could be exploited to gain elevated privileges, impacting all versions of CentOS 7 prior to 1708, Red Hat Enterprise Linux 7 before version 7.4, as well as all iterations of CentOS 6 and Red Hat Enterprise Linux 6, as noted in a recent advisory.
The flaw, which has been assigned a CVSS3 Base Score of 7.8 out of 10, involves the Linux kernel’s method for loading Executable and Linkable Format (ELF) binaries, leading to potential memory corruption. It is particularly concerning for unprivileged local users who have access to SUID or otherwise privileged Position Independent Executable (PIE) binaries, as they could leverage this vulnerability to elevate their privileges on affected systems.
To mitigate this vulnerability, users are advised to switch to a legacy memory mapping layout by setting the vm.legacy_va_layout to 1 in system configuration. This adjustment effectively disables the exploitation vector of this vulnerability by altering the way memory is allocated in the process address space, ensuring a safer distance between the PIE executable mapping and the reserved stack area.
Qualys further highlighted that the issue is not confined to PIEs with a read-write segment exceeding 128MB. Instead, even with smaller sizes, the risk persists, especially when passing large argument strings to the execve() call, as any PIE can be mapped below the stack and consequently trigger the vulnerability.
Linux distributions such as Red Hat, Debian, and CentOS have released security patches to remediate this flaw. The Qualys team has also indicated intentions to publish a proof-of-concept exploit targeting specific kernel versions in the near future. This follows a careful balancing of the time allowed for users to patch their systems before details about the exploit become widely available.
As the landscape of cybersecurity threats continues to evolve, it is imperative for organizations utilizing these Linux distributions to be proactive in addressing this vulnerability to mitigate the risk of a potential security breach. Adopting timely updates and understanding the mechanisms of exploitation will be critical in safeguarding sensitive data within affected environments.
In the context of the MITRE ATT&CK framework, tactics such as privilege escalation are particularly relevant in this case, highlighting the need for a solid understanding of local access methods and memory corruption vulnerabilities. As the cybersecurity landscape advances, maintaining awareness of such vulnerabilities is essential for business owners committed to protecting their systems against evolving cyber threats.
Stay vigilant and ensure your systems are up to date.