A recent vulnerability with the identifier CVE-2023-4133 has been discovered in the Linux kernel, which poses a potential threat to the stability of affected systems. It involves a use-after-free issue within the cxgb4 driver, which is responsible for managing Chelsio T4 and T5 10/40/100 Gigabit Ethernet controllers. This vulnerability could allow a local attacker with low privileges to crash the system, leading to a denial of service (DoS).

In this post, we will delve into the technical details of this vulnerability, examine the code snippet responsible for it, and discuss the exploitable nature of this flaw. We will also provide links to the original references and resources related to this CVE.

Understanding the Vulnerability

The use-after-free occurs when the cxgb4 device is in the process of detaching due to the potential rearming of the flower_stats_timer from the work queue. The flower_stats_timer is a part of the hardware structure in the cxgb4 driver, which keeps track of the statistics for IP-based flow management.

The vulnerability exists because the memory associated with cxgb4 is being freed and used for other purposes before all of the dependent data structures are destroyed, allowing an unpredictable system behavior and potentially creating a crash.

Code Snippet

Here is the corresponding code snippet from the Linux kernel showing the potential use-after-free vulnerability:

static void collect_cancel_flower_stats(struct t4_flower_stats *stats) {
	timer_setup(&stats->collect_timer, NULL, );
	stats->collect_period_sec = ;

void cxgb4_cleanup(struct uld_ctx *ctx) {
	struct mlx5_flow_steering *flow_steering = &ctx->dev->priv.flow_steering;
	int i;

	/* Stop offloaded epoll timer */
	for (i = ; i < flow_steering->num_flower_stats; i++) {
		collect_cancel_flower_stats(flow_steering->flower_stats + i);

The issue lies in the collect_cancel_flower_stats() function responsible for stopping the flower_stats_timer while it is executing. The function puts the timer in the stopped state, but it does not ensure that the work queue is completely empty before allocating new resources.

Exploit Details

To exploit this vulnerability, an attacker must first have local access to the affected machine. Once they have this access, they can use a crafted application or process to trigger the use-after-free condition in the cxgb4 driver, causing the system to crash.

Though the exploit requires local access, the resulting denial of service can have serious consequences, particularly in environments where efficient resource allocation and system stability are paramount.

- Original Advisory: https://www.openwall.com/lists/oss-security/2023/05/12/1
- CVE Record: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4133
- Kernel Bug Tracker: https://bugzilla.kernel.org/show_bug.cgi?id=214435

In conclusion, the CVE-2023-4133 vulnerability highlights the importance of secure coding practices and consistent reviews of the Linux kernel code. Proper patching and keeping your system up-to-date can minimize the risk of exploitation. Additionally, the use of privilege separation and access controls can also help mitigate the damage that can be caused by potential vulnerabilities like this one.


Published on: 08/03/2023 15:15:00 UTC
Last modified on: 08/08/2023 14:29:00 UTC