CVE-2021-27851 Explained : Impact and Mitigation

A security vulnerability labeled as CVE-2021-27851 has been discovered in 'guix-daemon' of GNU Guix. The vulnerability can lead to local privilege escalation in multi-user setups where 'guix-daemon' operates locally. The issue arises when an unprivileged user initiates a build process, creating a hardlink to a root-owned file, granting unauthorized write access to critical system files.

Understanding CVE-2021-27851

This section explores the critical details of the CVE-2021-27851 vulnerability.

What is CVE-2021-27851?

The vulnerability enables an unprivileged user to escalate privileges locally by exploiting the 'guix-daemon' process. By creating a hardlink to sensitive files, the user gains unauthorized write access to system resources.

The Impact of CVE-2021-27851

The vulnerability allows attackers to modify critical files, potentially leading to unauthorized access and control over the system. It poses a significant risk to system integrity and data confidentiality.

Technical Details of CVE-2021-27851

This section provides technical insights into the CVE-2021-27851 vulnerability.

Vulnerability Description

The vulnerability allows an unprivileged user to create hardlinks to root-owned files, providing unauthorized write access and potential exploitation of system resources.

Affected Systems and Versions

Versions equal to and higher than v0.11.0-3298-g2608e40988 and versions below v1.2.0-75109-g94f0312546 are susceptible to the CVE-2021-27851 vulnerability.

Exploitation Mechanism

Attackers take advantage of the 'guix-daemon' process in multi-user setups to create hardlinks to sensitive system files, leading to local privilege escalation.

Mitigation and Prevention

Here are essential steps to mitigate and prevent the CVE-2021-27851 vulnerability.

Immediate Steps to Take

Users should update 'guix-daemon' to a secure version and restrict unprivileged user access to critical system resources.

Long-Term Security Practices

Regularly monitor system logs, conduct security audits, and implement least privilege access to prevent unauthorized system alterations.

Patching and Updates

GNU Guix users are advised to apply the latest patches and updates to ensure system security and mitigate the risk of local privilege escalation.