CVE-2023-52919 - Linux Kernel NFC Vulnerability – NULL Pointer Dereference in send_acknowledge() Explored
In late 2023, security researchers found and patched a vulnerability in the Linux kernel’s NFC subsystem (specifically, the nci driver). This flaw, now tracked as CVE-2023-52919, could potentially lead to a system crash via a NULL pointer dereference. This post will walk you through what CVE-2023-52919 actually is, the buggy and fixed code, references for deeper reading, and how an exploit scenario might look. As always, we’ll keep things clear and easy to follow.
What is CVE-2023-52919?
CVE-2023-52919 is a vulnerability in the Linux kernel’s Near Field Communication (NFC) NCI core, specifically within the send_acknowledge() function. The vulnerability is a classic NULL pointer dereference—meaning the system might try to access memory that hasn’t been properly allocated, which leads to crashes or potentially more serious issues.
This problem happens if the kernel’s memory allocation function fails but is not checked. The function nci_skb_alloc() (which itself calls alloc_skb()) might return NULL on out-of-memory conditions. The original code didn't check for this, so it could pass a NULL SKU buffer pointer deeper, crashing the kernel.
Why is this important?
- Privilege: Local attacker, with code execution via NFC or manipulated input, could trigger a kernel NULL pointer dereference, leading to denial of service.
- Impact: System crash (kernel panic). While it’s not a privilege escalation or remote code execution, availability is a critical concern for server and IoT systems using NFC.
Below is a simplified snippet showing the problem in the NFC core
// Bad: vulnerable code before the fix
static int send_acknowledge(struct nci_dev *ndev)
{
struct sk_buff *skb;
skb = nci_skb_alloc(ndev, NCI_ACK_PKT_SIZE, GFP_KERNEL);
// <== returned skb could be NULL, but not checked!
// (later code)
nci_send_skb(ndev, skb); // if skb is NULL, crash!
return ;
}
If nci_skb_alloc() fails (due to memory pressure, for example) and returns NULL, the next code tries to use skb anyway. This leads to a NULL pointer dereference.
The fix is to actually check the return value and bail out if memory could not be allocated
// Good: fixed code
static int send_acknowledge(struct nci_dev *ndev)
{
struct sk_buff *skb;
skb = nci_skb_alloc(ndev, NCI_ACK_PKT_SIZE, GFP_KERNEL);
if (!skb) {
// Allocation failed, log and return error
pr_err("nfc: nci: send_acknowledge: alloc failed\n");
return -ENOMEM;
}
/* rest of the code */
nci_send_skb(ndev, skb);
return ;
}
This way, the code never passes a NULL pointer to nci_send_skb() and avoids crashing the kernel.
Main patch commit:
Bug report tracking:
- CVE-2023-52919 at NVD
- Bugzilla Linux Kernel Bug Report
NFC subsystem info:
Flood the system with crafted NFC requests to exhaust kernel memory.
- As soon as kernel memory allocation fails in this code path, the kernel panics due to the NULL pointer dereference.
Proof-of-Concept (Conceptual, not ready-to-run)
// This is just a conceptual example of what the exploit would target.
// It requires the ability to trigger NFC operations in the kernel.
for (int i = ; i < 100000; i++) {
trigger_nfc_acknowledge();
// Try to exhaust system memory and create an alloc failure
}
In practice, only privileged or local users can trigger such memory exhaustion, and the impact is denial of service.
How to Protect Yourself
- Patch your kernel: All major distros have patched this since late 2023 or early 2024. Look for kernel versions after late December 2023.
- Disable NFC if unused: As with any extra subsystem, disabling unused features closes attack surfaces.
Conclusion
CVE-2023-52919 reminds us how vital it is for kernel developers to check memory allocations—even for rare failure cases. If you use Linux with NFC features enabled (common in mobile, point-of-sale, and IoT), make sure your systems have received the patch for this vulnerability. Although it “only” causes a denial of service, stability is crucial for all Linux systems.
Stay patched, stay safe!
*This post was written for clarity and exclusive educational use. For full details, always consult original kernel sources and advisories.*
Timeline
Published on: 10/22/2024 08:15:02 UTC
Last modified on: 10/24/2024 03:53:16 UTC