CVE-2020-29479 : Exploit Details and Defense Strategies

An issue was discovered in Xen through 4.14.x. In the Ocaml xenstored implementation, the internal representation of the tree has special cases for the root node, leading to unprivileged guests being able to manipulate permissions and potentially cause denial of service.

Understanding CVE-2020-29479

This CVE highlights a vulnerability in the Xen hypervisor that allows unprivileged guests to exploit the Ocaml xenstored implementation.

What is CVE-2020-29479?

The issue arises from the lack of permission checks on certain operations related to the root node in the xenstored implementation.
Unprivileged guests can manipulate permissions, list, delete the root node, and potentially achieve xenstore write access.
Systems using oxenstored are vulnerable, while those using C xenstored are not affected.

The Impact of CVE-2020-29479

Unprivileged guests can modify permissions, list, and delete the root node, leading to a host-wide denial of service if the entire xenstore tree is deleted.
Exploiting this vulnerability can grant unauthorized write access to xenstore, compromising system integrity.

Technical Details of CVE-2020-29479

This section delves into the technical aspects of the vulnerability.

Vulnerability Description

The vulnerability allows unprivileged guests to manipulate permissions and access the root node without proper checks.

Affected Systems and Versions

All systems using oxenstored are vulnerable to this issue.
Systems using C xenstored are not impacted.

Exploitation Mechanism

Unprivileged guests can exploit the lack of permission checks to manipulate the root node and gain unauthorized access.

Mitigation and Prevention

Protecting systems from CVE-2020-29479 requires immediate actions and long-term security practices.

Immediate Steps to Take

Apply patches provided by Xen to address the vulnerability.
Monitor system logs for any suspicious activities related to xenstored.

Long-Term Security Practices

Regularly update and patch the Xen hypervisor to mitigate potential vulnerabilities.
Implement the principle of least privilege to restrict guest access and prevent unauthorized operations.

Patching and Updates

Stay informed about security advisories from Xen and promptly apply patches to secure the system.