CVE-2021-28715 : What You Need to Know

This article provides detailed information about CVE-2021-28715, a vulnerability that allows guests to force the Linux netback driver to hog large amounts of kernel memory.

Understanding CVE-2021-28715

This vulnerability relates to the Linux kernel's xen-netback backend driver, enabling guests to queue arbitrary amounts of network data, leading to an out-of-memory situation.

What is CVE-2021-28715?

Guests can manipulate the netback driver in Linux to accumulate excessive kernel memory, potentially causing a denial-of-service situation in the domain running the backend.

The Impact of CVE-2021-28715

The vulnerability can be exploited to exhaust memory resources in the hosting domain (dom0), affecting system stability and performance.

Technical Details of CVE-2021-28715

The vulnerability in the Linux kernel allows guests to circumvent measures meant to limit data accumulation, resulting in memory exhaustion.

Vulnerability Description

Incoming data packets intended for a guest can be buffered indefinitely, leading to a scenario where an excessive backlog of data is created, consuming significant kernel memory.

Affected Systems and Versions

All systems using the Linux kernel's xen-netback backend are vulnerable to this exploitation.

Exploitation Mechanism

Guests exploit the timeout mechanisms in the netback driver to accumulate excessive amounts of data, exploiting specific scenarios like UDP connections or requiring multiple free slots for packets.

Mitigation and Prevention

To address CVE-2021-28715, immediate actions and long-term security measures are necessary.

Immediate Steps to Take

Consider using alternative PV network backends like the qemu-based 'qnic' backend or setting up dedicated network driver domains per guest to mitigate the vulnerability.

Long-Term Security Practices

Regular monitoring, enforcing strict guest policies, and applying security updates promptly are essential to enhance system resilience.

Patching and Updates

Stay informed about security advisories and apply relevant patches and updates promptly to protect the system against potential attacks.