CVE-2024-55627

Executive Summary

CVE-2024-55627 is a high-severity vulnerability in Suricata, a widely used network Intrusion Detection System (IDS), Intrusion Prevention System (IPS), and Network Security Monitoring engine. The flaw resides in the TCP stream handling engine, where a specially crafted TCP stream can trigger an unsigned integer underflow. This underflow leads to a very large buffer overflow during the zero-filling (memset) initialization phase, potentially causing a denial of service (DoS) condition. The vulnerability affects all versions prior to 7.0.8. While no public proof-of-concept (PoC) or exploit code is currently available, the technical nature of the flaw makes it exploitable by an unauthenticated attacker sending malicious network traffic. The CVSS score of 5.9 (Medium) reflects the high availability impact but no confidentiality or integrity compromise.

Supply Chain & Package Security

Suricata is distributed as a standalone application, not as an NPM, PyPI, Go, or Ruby package. Therefore, supply chain package security considerations are not directly applicable. However, organizations using Suricata as part of a larger security stack should verify the integrity of their Suricata binaries or source code from official repositories.

CVSS Breakdown & Threat Level

• CVSS Score: 5.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required; a crafted TCP stream is sufficient.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – The vulnerability can cause a complete denial of service.

Threat Level: Medium. The lack of public exploit code and low EPSS score (0.0%) reduce immediate risk, but the ease of exploitation (network-based, no auth) and high availability impact warrant prompt patching.

Deep Dive & Mechanics

The vulnerability is rooted in the TCP stream reassembly logic within Suricata. When processing TCP segments, the engine allocates a buffer to hold the stream data. An unsigned integer underflow occurs when calculating the size of this buffer, specifically during the handling of certain crafted TCP options or sequence numbers. The underflow results in a very large (wrapping around to a huge positive value) buffer size. When memset is called to zero-fill this buffer, it attempts to write to an enormous memory region, causing a buffer overflow that corrupts adjacent memory and leads to a crash (DoS).

Root Cause: The flaw is in the calculation of the buffer length before the memset call. The code likely subtracts a value from an unsigned integer without proper bounds checking, leading to an underflow.

Trigger: A specially crafted TCP stream with specific sequence numbers, window sizes, or TCP options that cause the underflow condition.

Impact: Successful exploitation results in a denial of service of the Suricata process, potentially disabling network monitoring and intrusion detection capabilities.

Vulnerable vs. Patched Code

The vulnerable code (pre-7.0.8) likely resembles:

// Vulnerable code (conceptual)
uint32_t buffer_size = some_value - another_value; // Underflow if another_value > some_value
char *buffer = malloc(buffer_size);
memset(buffer, 0, buffer_size); // Overflow due to huge buffer_size

The patched code (7.0.8) adds a bounds check:

// Patched code (conceptual)
uint32_t buffer_size;
if (another_value > some_value) {
    buffer_size = 0; // or handle error
} else {
    buffer_size = some_value - another_value;
}
char *buffer = malloc(buffer_size);
if (buffer) {
    memset(buffer, 0, buffer_size);
}

The exact fix involves validating the subtraction result to prevent underflow.

Exploitation & Lab Setup

Red Team (Offensive)

Note: No public exploit code is available. The following is a conceptual approach for lab testing.

1. Lab Environment:

   • Attacker: Kali Linux with scapy or hping3.
   • Target: Ubuntu 22.04 running Suricata 7.0.7 (vulnerable) in IDS mode.
   • Network: Both machines on the same subnet.

2. Crafting the Malicious TCP Stream:

   • Use scapy to send a TCP packet with specific sequence numbers and options designed to trigger the underflow.
   • Example (conceptual):

     from scapy.all import *
     ip = IP(src="192.168.1.100", dst="192.168.1.200")
     tcp = TCP(sport=12345, dport=80, flags="S", seq=0, options=[(2, b'\x00'*100)])  # Malicious options
     send(ip/tcp)
     

   • The exact payload would need to be reverse-engineered from the Suricata source code.

3. Verification:

   • Monitor Suricata logs (/var/log/suricata/suricata.log) for crashes.
   • Check if the Suricata process terminates unexpectedly.

Blue Team (Defensive)

1. Detection:

   • Monitor for unusual TCP packets with malformed options or extreme sequence numbers.
   • Use network flow analysis to detect anomalies in TCP stream reassembly.

2. Mitigation:

   • Immediately upgrade to Suricata 7.0.8 or later.
   • If patching is delayed, consider deploying a network firewall to filter suspicious TCP traffic.
   • Enable Suricata's built-in anomaly detection rules (if available).

3. Hunting:

   • Search for logs indicating Suricata crashes or restarts.
   • Analyze packet captures for TCP streams with unusual characteristics.

Indicators of Compromise (IOCs)

• Network:
  • TCP packets with malformed options (e.g., excessive length or invalid values).
  • TCP segments with sequence numbers that cause reassembly errors.
  • Sudden termination of Suricata process.
• Host:
  • Suricata crash logs in /var/log/suricata/.
  • Core dumps from Suricata.
  • High memory usage before crash (due to buffer overflow).

Detection Engineering

YARA Rule

rule CVE_2024_55627_Suricata_TCP_Underflow {
    meta:
        description = "Detects potential exploitation of CVE-2024-55627 via crafted TCP streams"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-55627"
    strings:
        $tcp_option_malformed = { 02 [0-1] (FF | FE) }  // Example: TCP option type 2 with invalid length
    condition:
        $tcp_option_malformed
}

Sigma Rule

title: Suricata CVE-2024-55627 Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects network traffic attempting to exploit CVE-2024-55627 in Suricata
author: Valters IT
date: 2025/04/10
logsource:
    category: network
    product: suricata
detection:
    selection:
        event_type: alert
        alert.signature_id: 202455627
    condition: selection
falsepositives:
    - Legitimate but unusual TCP streams
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-55627 Potential Exploit - Malformed TCP Options"; flow:to_server; content:"|02|"; depth:1; offset:20; byte_test:1,<,2,1; sid:202455627; rev:1;)

Remediation & Mitigation

1. Immediate Action:

   • Upgrade Suricata to version 7.0.8 or later. This is the only complete fix.
   • Download from official Suricata repository: https://suricata.io/download/

2. Workarounds (if patching is delayed):

   • Deploy network intrusion prevention systems (IPS) to block suspicious TCP streams.
   • Use firewall rules to limit traffic to trusted sources.
   • Monitor Suricata logs for crashes and restart the service automatically.

3. Long-term:

   • Implement a vulnerability management program to ensure timely patching.
   • Regularly review Suricata configuration and enable anomaly detection features.

Valters IT Signature:
This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.