Linux Kernel, Memory Leak Vulnerability, CVE-2025-21788 (Critical)

How the Mentioned CVE Works:

CVE-2025-21788 is a critical memory leak vulnerability in the Linux kernel, specifically within the `am65-cpsw` Ethernet driver. The issue arises when the driver processes XDP (eXpress Data Path) packets. The `am65_cpsw_build_skb()` function allocates memory for an SKB (socket buffer) before evaluating the XDP program’s result. If the XDP program returns any action other than `XDP_PASS` (e.g., XDP_DROP), the allocated memory is not freed, leading to a memory leak. This vulnerability can be exploited to exhaust system memory, causing denial of service (DoS). The fix involves moving the SKB allocation after the XDP program evaluation, ensuring memory is only allocated when necessary.

DailyCVE Form:

Platform: Linux Kernel
Version: am65-cpsw Ethernet Driver
Vulnerability: Memory Leak
Severity: Critical
Date: 02/26/2025

(End of form)

What Undercode Say:

Analytics:

Impact: Memory exhaustion leading to system crashes or DoS.
Exploitability: Requires local or remote access to send crafted XDP packets.
Prevalence: Affects systems using the `am65-cpsw` driver with XDP enabled.

Commands:

1. Check if the `am65-cpsw` driver is loaded:

lsmod | grep am65_cpsw

2. Disable XDP temporarily to mitigate:

ethtool -K <interface> xdp off

3. Monitor memory usage for leaks:

watch -n 1 "cat /proc/meminfo | grep MemFree"

Code:

Vulnerable code snippet (before fix):

skb = am65_cpsw_build_skb();
xdp_result = bpf_prog_run_xdp(xdp_prog, xdp);
if (xdp_result != XDP_PASS) {
// Memory leak occurs here
return;
}

Patched code snippet (after fix):

xdp_result = bpf_prog_run_xdp(xdp_prog, xdp);
if (xdp_result == XDP_PASS) {
skb = am65_cpsw_build_skb();
}

URLs:

Kernel.org patch details: https://www.kernel.org/
XDP documentation: https://docs.cilium.io/en/stable/bpf/xdp
NVD entry for CVE-2025-21788: https://nvd.nist.gov/vuln/detail/CVE-2025-21788

Protection:

Update the Linux kernel to the latest version containing the patch.
Avoid using XDP on vulnerable systems until patched.
Implement memory usage monitoring to detect potential leaks.

Exploitation:

Craft malicious XDP packets to trigger the memory leak:

from scapy.all import
packet = Ether() / IP() / UDP()
sendp(packet, iface="eth0", count=100000)

Use tools like `perf` to analyze kernel memory usage during exploitation:
```
perf stat -e kmem:kmalloc -e kmem:kfree
```

References:

Reported By: https://nvd.nist.gov/vuln/detail/CVE-2025-21788
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