Overview
In our digital era, the security of the Linux kernel is of paramount importance due to its widespread usage by businesses and individuals alike. A newly discovered vulnerability, known as CVE-2021-47670, threatens this security. This vulnerability could potentially lead to system compromise or data leakage, making it a significant concern for all Linux users.
This blog post aims to provide an in-depth understanding of CVE-2021-47670, its potential impact, and how it can be mitigated. The vulnerability primarily affects the Linux kernel and arises from a use-after-free bug in the peak_usb module.
Vulnerability Summary
CVE ID: CVE-2021-47670
Severity: High (7.8 CVSS score)
Attack Vector: Local
Privileges Required: Low
User Interaction: None
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
Linux Kernel | Up to 5.13.19
How the Exploit Works
The vulnerability arises from the unsafe dereferencing of the socket buffer (skb) after calling peak_usb_netif_rx_ni(skb). Specifically, the can_frame cf, which aliases the skb memory is accessed after the peak_usb_netif_rx_ni(). This leads to a use-after-free condition, which can then be exploited to execute arbitrary code or cause a denial of service.
Conceptual Example Code
While the exact exploit code may differ based on the specific circumstances, the following is a conceptual example in pseudocode of how the vulnerability might be exploited:
// Allocate socket buffer
struct sk_buff *skb = alloc_skb(...);
// Fill the buffer with data
...
// Call peak_usb_netif_rx_ni(), which frees the socket buffer
peak_usb_netif_rx_ni(skb);
// Access the freed buffer, leading to a use-after-free condition
struct can_frame *cf = (struct can_frame *)skb->data;Note: This example is for illustrative purposes only and does not represent a working exploit.
Mitigation Guidance
The recommended mitigation for this vulnerability is to apply the vendor-provided patch. This will resolve the vulnerability by reordering the lines involved in the issue. However, as a temporary mitigation, using a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) can also help to detect and prevent exploitation attempts.