CVE-2024-55626

Executive Summary

CVE-2024-55626 is a buffer overflow vulnerability in Suricata, a widely used network Intrusion Detection System (IDS), Intrusion Prevention System (IPS), and Network Security Monitoring engine. The flaw is triggered when a large BPF (Berkeley Packet Filter) filter file is provided to Suricata at startup. This can lead to a buffer overflow condition, potentially causing a denial of service (DoS) by crashing the Suricata process. The vulnerability is rated with a CVSS score of 3.3 (Low), indicating a low severity due to the requirement of local access and the limited impact on availability. The issue has been addressed in Suricata version 7.0.8.

Supply Chain & Package Security

Suricata is distributed as a standalone application, not through package managers like NPM, PyPI, Go, or Ruby. Therefore, supply chain security concerns are minimal. However, users should ensure they obtain Suricata from official sources (e.g., the Suricata GitHub repository or official package repositories) to avoid tampered binaries.

CVSS Breakdown & Threat Level

• CVSS Score: 3.3 (Low)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Attack Vector (AV): Local (L) – The attacker must have local access to the system to provide a malicious BPF file.
• Attack Complexity (AC): Low (L) – No special conditions or mitigations are required.
• Privileges Required (PR): None (N) – No privileges are needed to trigger the vulnerability.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data is exposed.
• Integrity (I): None (N) – No data is modified.
• Availability (A): Low (L) – The vulnerability can cause a denial of service (crash) of the Suricata process.

Threat Level: Low. The vulnerability requires local access and only impacts availability. It is not remotely exploitable.

Deep Dive & Mechanics

The vulnerability resides in the BPF filter loading mechanism of Suricata. BPF filters are used to define which network packets should be captured or inspected. When Suricata starts, it reads a BPF filter file specified by the user. The issue is a classic buffer overflow: the code does not properly validate the size of the BPF filter data before copying it into a fixed-size buffer. If an attacker provides a BPF filter file larger than the expected buffer size, the excess data overwrites adjacent memory, potentially causing a crash or, in more sophisticated scenarios, arbitrary code execution (though this is unlikely given the low CVSS score and the nature of the vulnerability).

The vulnerable code path is in the BPF filter parsing routine. The buffer used to store the filter is allocated with a fixed size, and the memcpy or similar function does not check the source data length against the destination buffer size. This leads to a stack-based or heap-based buffer overflow, depending on the implementation.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-7.0.8):

// Simplified example of vulnerable BPF loading
#define MAX_BPF_SIZE 1024
char bpf_buffer[MAX_BPF_SIZE];
read_bpf_file(bpf_file_path, bpf_buffer, sizeof(bpf_buffer)); // No size check

Patched Code (7.0.8):

// Patched version with size validation
#define MAX_BPF_SIZE 1024
char bpf_buffer[MAX_BPF_SIZE];
size_t file_size = get_file_size(bpf_file_path);
if (file_size > MAX_BPF_SIZE) {
    // Handle error: file too large
    return -1;
}
read_bpf_file(bpf_file_path, bpf_buffer, file_size); // Safe copy

The patch adds a check to ensure the BPF file size does not exceed the buffer capacity before reading it.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Local access to a system running Suricata < 7.0.8.
• Ability to write a BPF filter file to a location that Suricata will read at startup (e.g., via command-line argument or configuration file).

Exploitation Steps:

1. Create a malicious BPF filter file larger than the expected buffer size (e.g., 10KB).
2. Place the file in a location accessible to Suricata.
3. Start Suricata with the malicious BPF file: suricata -F malicious_bpf_file
4. Suricata will crash due to the buffer overflow, causing a denial of service.

Example Malicious BPF File Generation (Python):

#!/usr/bin/env python3
# Generate a large BPF filter file to trigger CVE-2024-55626
with open('malicious_bpf.bpf', 'wb') as f:
    f.write(b'\x00' * 10000)  # 10KB of zeros
print("Malicious BPF file created: malicious_bpf.bpf")

Blue Team (Defender)

Detection:

• Monitor Suricata startup logs for crashes or errors related to BPF loading.
• Use file integrity monitoring to detect unauthorized modifications to BPF filter files.
• Implement system call monitoring to detect abnormal memory operations.

Prevention:

• Upgrade to Suricata 7.0.8 or later.
• Restrict write access to BPF filter files to authorized users only.
• Validate BPF file sizes before passing them to Suricata.

Hunting:

• Search for Suricata crash dumps or core files.
• Analyze system logs for Suricata startup failures.

Indicators of Compromise (IOCs)

• File: Malicious BPF filter files with unusually large sizes (e.g., > 1KB).
• Log Entry: Suricata crash logs containing "BPF" or "buffer overflow" errors.
• Process: Suricata process terminating unexpectedly with a segmentation fault.
• Network: No network-based IOCs, as the vulnerability is local.

Detection Engineering

YARA Rule

rule CVE_2024_55626_BPF_Overflow {
    meta:
        description = "Detects malicious BPF files targeting CVE-2024-55626"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-55626"
    strings:
        $bpf_magic = { 28 00 00 00 }  // BPF magic number (little-endian)
        $large_size = { 00 10 00 00 } // Size > 4096 bytes (example)
    condition:
        $bpf_magic at 0 and filesize > 4096
}

Sigma Rule

title: Suricata BPF Buffer Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2024-55626 by loading a large BPF file into Suricata
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/suricata'
        CommandLine|contains: '-F'
    condition: selection
falsepositives:
    - Legitimate use of large BPF filters
level: low

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-55626 BPF Overflow Attempt"; flow:to_server; content:"|28 00 00 00|"; offset:0; depth:4; byte_test:4,>,4096,0; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Suricata to version 7.0.8 or later.
2. If upgrade is not possible, restrict access to BPF filter files to trusted users only.
3. Monitor Suricata logs for crashes or errors.

Long-Term Measures:

• Implement input validation for all configuration files.
• Use memory-safe programming practices (e.g., bounds checking).
• Regularly update Suricata to the latest version.

Workarounds:

• Avoid using BPF filters if not necessary.
• Use a wrapper script to validate BPF file size before passing to Suricata.

Valters IT
Securing Digital Frontiers