CVE-2018-18955 : What You Need to Know

A privilege escalation vulnerability in the Linux kernel versions 4.15.x through 4.19.x before 4.19.2 has been identified, allowing attackers to bypass access controls and gain unauthorized access to sensitive files.

Understanding CVE-2018-18955

What is CVE-2018-18955?

The vulnerability exists in the map_write() function within the kernel/user_namespace.c file, specifically mishandling nested user namespaces with more than 5 UID or GID ranges. An attacker with CAP_SYS_ADMIN privilege in the affected user namespace can exploit this flaw.

The Impact of CVE-2018-18955

The vulnerability enables attackers to bypass access controls on resources outside the namespace, potentially leading to unauthorized access to critical files like /etc/shadow. The issue arises from a failure in applying ID transformations properly.

Technical Details of CVE-2018-18955

Vulnerability Description

The flaw in map_write() allows privilege escalation due to mishandling of nested user namespaces with multiple UID or GID ranges.

Affected Systems and Versions

Linux kernel versions 4.15.x through 4.19.x before 4.19.2

Exploitation Mechanism

Attackers with CAP_SYS_ADMIN privilege in the affected user namespace can exploit the vulnerability to bypass access controls and gain unauthorized access to sensitive files.

Mitigation and Prevention

Immediate Steps to Take

Apply the necessary patches provided by the Linux kernel maintainers.
Monitor for any unauthorized access to critical files.

Long-Term Security Practices

Regularly update the Linux kernel to the latest stable version.
Implement least privilege access controls to limit the impact of potential vulnerabilities.

Patching and Updates

Ensure timely installation of security patches and updates to mitigate the risk of exploitation.