How the CVE Works
The vulnerability occurs in the Linux kernel’s UDP stack when handling socket buffer memory accounting. The issue arises due to improper handling of signed integers in `sk->sk_rmem_alloc` (receive memory allocation counter) and `sk->sk_rcvbuf` (receive buffer size). If `sk->sk_rcvbuf` is set to INT_MAX, the condition `atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf` becomes ineffective, allowing `sk->sk_rmem_alloc` to wrap around repeatedly when large UDP packets are received. This leads to memory corruption, enabling an attacker to exhaust kernel memory or trigger undefined behavior.
The flaw was introduced when a previous boundary check for `INT_MAX` was removed, making the system vulnerable to integer overflow. Attackers can exploit this by flooding a UDP socket with specially crafted packets, bypassing memory limits and potentially causing a denial of service (DoS) or arbitrary code execution.
DailyCVE Form
Platform: Linux Kernel
Version: Pre-patch versions
Vulnerability: Integer Overflow
Severity: Critical
Date: 2025-04-16
What Undercode Say:
Exploitation:
1. Trigger Condition:
- Set `sk->sk_rcvbuf` to `INT_MAX` via
SO_RCVBUF. - Flood the target UDP socket with packets exceeding kernel memory limits.
2. Exploit Code (Conceptual):
int sock = socket(AF_INET, SOCK_DGRAM, 0); int rcvbuf = INT_MAX; setsockopt(sock, SOL_SOCKET, SO_RCVBUF, &rcvbuf, sizeof(rcvbuf)); send_exploit_packets(sock); // Flood with oversized UDP packets
3. Post-Exploit Impact:
- Kernel memory exhaustion.
- Possible privilege escalation via memory corruption.
Mitigation:
1. Patch Application:
sudo apt update && sudo apt upgrade linux-image-$(uname -r)
2. Temporary Workaround:
sysctl -w net.core.rmem_max=8388608 Limit max receive buffer sysctl -w net.core.udp_mem="32768 65536 262144" Restrict UDP memory
3. Detection Command:
grep -i "udp_mem" /etc/sysctl.conf ss -uam | grep -i "UNCONN.skmem"
4. Kernel Debugging:
dmesg | grep -i "udp.overflow" perf probe -x /lib/modules/$(uname -r)/kernel/net/ipv4/udp.c '__udp_enqueue_schedule_skb'
5. Memory Monitoring:
watch -n 1 "cat /proc/net/sockstat | grep UDP"
6. Exploit Prevention:
// Kernel patch pseudocode if (atomic_read(&sk->sk_rmem_alloc) + size > INT_MAX) goto drop;
7. Network Hardening:
iptables -A INPUT -p udp --dport <port> -m length --length 1000:65535 -j DROP
8. Logging Suspicious Activity:
auditctl -a always,exit -F arch=b64 -S socket -F a0=2 -F success=1 -k UDP_EXPLOIT_ATTEMPT
9. Forensics Analysis:
crash /proc/kcore -c "struct sock.sk_rmem_alloc"
10. Final Advisory:
- Apply kernel updates immediately.
- Restrict UDP buffer sizes via
sysctl. - Monitor kernel logs for memory anomalies.
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
