How the CVE Works:
CVE-2025-21762 is a critical use-after-free (UAF) vulnerability in the Linux kernel’s ARP (Address Resolution Protocol) implementation. The issue arises in the `arp_xmit()` function, which is responsible for transmitting ARP packets. This function can be called without proper synchronization mechanisms like RTNL (Routing Netlink) or RCU (Read-Copy-Update) protection. As a result, a race condition can occur where a memory region is accessed after it has been freed, leading to potential exploitation. Attackers could leverage this vulnerability to execute arbitrary code, escalate privileges, or cause a denial-of-service (DoS) condition.
The vulnerability is particularly dangerous because ARP is a fundamental networking protocol used to map IP addresses to MAC addresses. Exploiting this flaw could allow an attacker to manipulate network traffic or disrupt communication between devices on a local network. The CVSS 4.0 score reflects its critical severity due to the potential for widespread impact.
DailyCVE Form:
Platform: Linux Kernel
Version: Pre-5.15.90
Vulnerability: Use-After-Free
Severity: Critical
Date: 02/26/2025
What Undercode Say:
Exploitation:
1. Exploit Code:
// Hypothetical PoC for CVE-2025-21762
include <linux/if_arp.h>
include <linux/netdevice.h>
include <linux/skbuff.h>
void exploit_arp_xmit() {
struct sk_buff skb = alloc_skb(64, GFP_KERNEL);
struct net_device dev = dev_get_by_name(&init_net, "eth0");
arp_xmit(skb, dev, ETH_P_ARP, NULL, NULL, NULL);
// Trigger UAF by freeing skb prematurely
kfree_skb(skb);
}
2. Exploit Steps:
- Craft malicious ARP packets to trigger the race condition.
- Exploit the UAF to overwrite kernel memory.
- Gain elevated privileges or cause a kernel panic.
Protection:
1. Patch Application:
Update to Linux kernel version 5.15.90 or later, which includes the fix for this vulnerability.
2. Mitigation Commands:
sudo apt-get update sudo apt-get install linux-image-5.15.90-generic sudo reboot
3. Kernel Hardening:
Enable kernel hardening features like KASLR (Kernel Address Space Layout Randomization) and SMAP (Supervisor Mode Access Prevention).
4. Monitoring:
Use tools like `auditd` to monitor ARP-related system calls and detect suspicious activity.
5. Network Segmentation:
Isolate critical systems to minimize the impact of potential ARP spoofing attacks.
6. Code Review:
Review kernel code for similar synchronization issues in other networking functions.
7. Debugging:
Use `gdb` or `kprobes` to trace the `arp_xmit()` function and identify potential race conditions.
8. Log Analysis:
Analyze kernel logs (dmesg) for signs of memory corruption or crashes.
9. Disable ARP:
In controlled environments, consider disabling ARP if not required.
10. Community Reporting:
Report any suspicious activity or potential exploits to the Linux kernel security team.
By following these steps, administrators can mitigate the risks associated with CVE-2025-21762 and protect their systems from potential exploitation.
References:
Reported By: https://nvd.nist.gov/vuln/detail/CVE-2025-21762
Extra Source Hub:
Undercode
