CVE-2026-11915

Executive Summary

CVE-2026-11915 describes a vulnerability in Drupal’s Brute Force Attack Protection mechanism. The official description is minimal, stating only that the issue affects all versions of the Brute Force Attack Protection component. No CVSS score, CWE, or technical details have been published. The EPSS score is 0.0%, indicating no observed exploitation in the wild. No public proof-of-concept, exploit code, or patch information is available. This report provides a structured analysis based on the limited data, focusing on potential attack vectors, detection strategies, and mitigation recommendations for Drupal environments.

Supply Chain & Package Security

Drupal is a PHP-based content management system. The Brute Force Attack Protection component is part of the core Drupal security modules. Since no specific package version or repository is identified, supply chain risks cannot be assessed. Administrators should ensure all Drupal core and contributed modules are updated to the latest stable versions.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unscored)
• CVSS Vector: UNKNOWN
• Severity: Unassigned
• Attack Vector: Unknown
• Attack Complexity: Unknown
• Privileges Required: Unknown
• User Interaction: Unknown
• Scope: Unknown
• Confidentiality Impact: Unknown
• Integrity Impact: Unknown
• Availability Impact: Unknown

Due to the lack of scoring data, the threat level cannot be determined. However, brute force protection vulnerabilities typically affect authentication mechanisms and could lead to account takeover or denial of service.

Deep Dive & Mechanics

The vulnerability resides in Drupal’s Brute Force Attack Protection module, which is designed to limit login attempts and prevent automated password guessing. The exact flaw is unspecified, but common issues in such modules include:

• Bypass of rate limiting: Attackers may circumvent IP-based or cookie-based throttling by manipulating headers or using distributed attack sources.
• Incorrect lockout logic: Flawed time windows or reset conditions could allow unlimited attempts.
• Race conditions: Concurrent requests might bypass lockout checks.
• Information disclosure: Error messages or response timing could reveal valid usernames.

Without detailed CVE data, these are hypothetical scenarios based on typical brute force protection weaknesses.

Vulnerable vs. Patched Code

No code samples are available because the vulnerability details and patch are not public. In general, a vulnerable implementation might look like:

// Vulnerable: No rate limiting check
function login_attempt($username, $password) {
    // Direct authentication without throttling
    return authenticate($username, $password);
}

A patched version would include:

// Patched: Rate limiting applied
function login_attempt($username, $password) {
    if (is_rate_limited($username, $_SERVER['REMOTE_ADDR'])) {
        return ['error' => 'Too many attempts'];
    }
    return authenticate($username, $password);
}

Exploitation & Lab Setup

Red Team

Since no exploit code is available, a red team would need to reverse-engineer the Drupal brute force protection logic. A typical approach involves:

1. Identify the login endpoint (e.g., /user/login).
2. Send rapid authentication requests using tools like Hydra or custom Python scripts.
3. Monitor responses for lockout messages or timing differences.
4. Attempt bypass techniques such as:
   • Using different IP addresses via proxies or VPNs.
   • Manipulating X-Forwarded-For headers.
   • Sending requests with randomized user agents.
   • Exploiting race conditions with concurrent requests.

Example Python script for testing:

import requests
import threading

url = "https://target.com/user/login"
payload = {"name": "admin", "pass": "password"}

def attempt():
    r = requests.post(url, data=payload)
    print(r.status_code, r.text[:100])

threads = []
for i in range(100):
    t = threading.Thread(target=attempt)
    threads.append(t)
    t.start()

for t in threads:
    t.join()

Blue Team

Blue team detection should focus on:

1. Monitor login endpoints for high request rates from single IPs or user agents.
2. Alert on failed login spikes (e.g., >10 failures per minute per user).
3. Correlate with IP reputation using threat intelligence feeds.
4. Enable Drupal’s built-in logging and review watchdog logs.
5. Deploy WAF rules to block suspicious patterns.

Indicators of Compromise (IOCs)

No specific IOCs are available. General indicators of brute force attacks include:

• IP addresses with high failed login rates (e.g., >50 attempts in 5 minutes).
• User agents that are non-standard or repeated across many requests.
• Timing patterns showing automated, rapid requests.
• Log entries with repeated access denied or login failed messages.

Example IOC list (hypothetical):

192.168.1.100
10.0.0.50
Mozilla/5.0 (compatible; BruteForceBot/1.0)

Detection Engineering

YARA Rule

rule Detect_Drupal_BruteForce_Attempts {
    meta:
        description = "Detects rapid login attempts to Drupal login endpoint"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2026-11915"
    strings:
        $login_path = "/user/login"
        $failed_msg = "unrecognized username or password"
        $lockout_msg = "too many login attempts"
    condition:
        # of ($failed_msg) > 10 or $lockout_msg
}

Sigma Rule

title: Drupal Brute Force Attack Protection Bypass Attempt
id: drupal-brute-force-bypass
status: experimental
description: Detects multiple failed login attempts to Drupal login endpoint
logsource:
    category: web
    product: drupal
detection:
    selection:
        cs_uri_stem: "/user/login"
        sc_status: 403
    timeframe: 5m
    condition: selection | count() > 10
falsepositives:
    - Legitimate users forgetting passwords
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-11915 Drupal Brute Force Attack Protection Bypass";
    flow:to_server;
    content:"POST"; http_method;
    content:"/user/login"; http_uri;
    threshold: type both, track by_src, count 10, seconds 300;
    classtype:attempted-user;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

1. Apply official patches as soon as they are released by Drupal.
2. Update Drupal core to the latest version (currently 10.x or 11.x).
3. Enable and configure the Brute Force Attack Protection module properly.
4. Implement additional rate limiting at the web server or WAF level.
5. Use strong password policies and multi-factor authentication.
6. Monitor logs for unusual login activity.
7. Restrict access to the login page via IP whitelisting if possible.

Valters IT
DevSecOps & Cyber Threat Intelligence Division
Report generated for CVE-2026-11915