How the Mentioned CVE Works:
CVE-2025-21763 is a critical use-after-free (UAF) vulnerability in the Linux kernel, specifically within the `__neigh_notify()` function. This function is responsible for notifying neighboring nodes about changes in the network state. The issue arises when `__neigh_notify()` is called without proper RCU (Read-Copy-Update) or RTNL (Routing Netlink) protection, leading to a potential use-after-free scenario. An attacker could exploit this vulnerability to execute arbitrary code, escalate privileges, or cause a denial of service (DoS) by manipulating network neighbor tables. The lack of RCU protection allows freed memory to be accessed, resulting in undefined behavior and potential system compromise.
DailyCVE Form:
Platform: Linux Kernel
Version: Up to 5.15.90
Vulnerability: Use-After-Free
Severity: Critical
Date: 02/26/2025
What Undercode Say:
Exploitation:
1. Exploit Code Example:
struct neighbour neigh;
neigh = __neigh_lookup(&arp_tbl, target_ip, dev, 1);
if (neigh) {
neigh_update(neigh, NULL, NUD_FAILED, 0, 0);
// Trigger UAF by accessing freed memory
}
2. Steps to Exploit:
- Identify a target system running a vulnerable Linux kernel version.
- Craft a malicious packet to manipulate the neighbor table.
- Trigger the UAF by forcing `__neigh_notify()` to access freed memory.
- Execute arbitrary code or crash the system.
Protection:
1. Patch Application:
- Apply the official kernel patch from the Linux kernel repository.
- Update to kernel version 5.15.91 or later.
2. Mitigation Commands:
- Disable unnecessary network protocols:
sudo sysctl -w net.ipv4.conf.all.arp_ignore=1 sudo sysctl -w net.ipv4.conf.all.arp_announce=2
- Restrict access to
/proc/sys/net/ipv4/neigh:sudo chmod 600 /proc/sys/net/ipv4/neigh/
3. Monitoring:
- Use `dmesg` to monitor kernel logs for suspicious activity:
dmesg | grep "neighbour"
- Implement kernel hardening tools like `grsecurity` or
SELinux.
4. Detection Script:
!/bin/bash if uname -r | grep -q "5.15.90"; then echo "Vulnerable kernel detected. Apply patches immediately." else echo "System is not vulnerable." fi
5. References:
- Kernel Patch: bash
- CVE Details: bash
By following these steps, you can exploit or protect against CVE-2025-21763 effectively. Always prioritize patching and system hardening to mitigate such vulnerabilities.
References:
Reported By: https://nvd.nist.gov/vuln/detail/CVE-2025-21763
Extra Source Hub:
Undercode
