CVE-2023-4921 Explained : Impact and Mitigation

This CVE involves a use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq component, allowing for local privilege escalation.

Understanding CVE-2023-4921

This vulnerability in the Linux kernel's net/sched: sch_qfq component can be exploited by an attacker to escalate their privileges on the system.

What is CVE-2023-4921?

The CVE-2023-4921 vulnerability is classified as a use-after-free issue within the Linux kernel's net/sched: sch_qfq component. Exploiting this vulnerability enables an attacker to escalate their privileges locally. Specifically, when the plug qdisc is used as a class of the qfq qdisc, sending network packets triggers the use-after-free in qfq_dequeue() due to the incorrect .peek handler of sch_plug and the lack of error checking in agg_dequeue().

The Impact of CVE-2023-4921

The impact of CVE-2023-4921 is categorized as privilege escalation (CAPEC-233), where an attacker could potentially elevate their privileges on the affected system, thereby gaining unauthorized access to sensitive information or performing malicious actions.

Technical Details of CVE-2023-4921

This section provides detailed technical information about the vulnerability to help understand its nature and implications.

Vulnerability Description

The vulnerability arises from a use-after-free flaw in the Linux kernel's net/sched: sch_qfq component, which can be triggered by specific network packet interactions. Exploiting this flaw can lead to local privilege escalation on the system.

Affected Systems and Versions

The affected vendor is Linux, specifically the Kernel package, with versions ranging from 3.8 to less than 6.6 identified as vulnerable. It is important to note that the default status is marked as unaffected for this vulnerability.

Exploitation Mechanism

Exploiting this vulnerability requires sending network packets to trigger the use-after-free in the qfq_dequeue() function due to specific conditions related to sch_plug and agg_dequeue().

Mitigation and Prevention

To protect systems from the CVE-2023-4921 vulnerability and prevent potential exploitation, certain mitigation and prevention measures should be taken.

Immediate Steps to Take

It is crucial to apply the recommended patch provided by the Linux kernel maintainers to address the use-after-free vulnerability.
Upgrading to a version beyond commit 8fc134fee27f2263988ae38920bc03da416b03d8 is advised to mitigate the risk of privilege escalation.

Long-Term Security Practices

Ensure regular monitoring of security advisories and updates from the Linux kernel maintainers to stay informed about potential vulnerabilities and their fixes.

Patching and Updates

Regularly update and patch the Linux kernel to include the latest security enhancements and fixes, reducing the risk of exploitation from known vulnerabilities like CVE-2023-4921.