CVE-2026-107256 in Shield Plugin
Summary
by MITRE • 10/30/2026
Improper Restriction of Excessive Authentication Attempts vulnerability in Drupal Shield allows Brute Force. This issue affects Shield versions: from 0.0.0 to 1.9.0.
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Analysis
by VulDB Data Team • 10/30/2026
The Drupal module known as Shield, specifically within version ranges extending from the initial release up through version 1.9.0, contains a critical security flaw classified under CWE-307, which denotes Improper Restriction of Excessive Authentication Attempts. This vulnerability fundamentally undermines the integrity of access control mechanisms by failing to implement adequate rate limiting or account lockout policies for authentication endpoints. In a typical secure implementation, systems are designed to detect and mitigate repetitive login failures through temporary account suspension, CAPTCHA challenges, or progressive delays in response times. However, the absence of these protective measures in this specific iteration of Shield leaves user credentials exposed to automated exploitation techniques that rely on high-volume credential stuffing or brute force attacks.
From a technical perspective, the flaw resides in the module's handling of authentication requests where no threshold is established for consecutive failed login attempts within a defined time window. This allows an attacker to submit thousands of password guesses against valid usernames without triggering any defensive responses such as IP-based throttling or user account locking. The lack of exponential backoff mechanisms further exacerbates the risk, enabling rapid-fire automated scripts to test large dictionaries of common passwords against targeted accounts with minimal latency between attempts. This architectural oversight effectively neutralizes standard defenses that rely on behavioral analysis of authentication patterns to identify malicious activity.
The operational impact of this vulnerability is severe, particularly for Drupal sites where Shield is deployed as a primary or supplementary access control layer. Attackers can leverage automated tools like Hydra or Medusa to systematically guess credentials, potentially gaining unauthorized administrative privileges if weak passwords are in use. Successful exploitation leads directly to CWE-287, Improper Authentication, and often cascades into subsequent attacks such as data exfiltration, defacement, or the installation of web shells for persistent access. Given that Drupal is widely used by enterprises and government entities, this vulnerability poses a significant risk to sensitive information integrity and availability, potentially resulting in regulatory non-compliance under frameworks like GDPR or HIPAA due to unauthorized data exposure.
In alignment with industry threat modeling standards such as MITRE ATT&CK, this vulnerability facilitates the T1110 technique of Brute Force attacks. The absence of detection logic for excessive authentication failures means that security information and event management systems may not generate appropriate alerts unless external network-level controls are in place. This gap allows attackers to operate stealthily during the initial compromise phase, as traditional intrusion prevention systems might not flag individual login attempts if they do not exceed a certain volume threshold at the network layer alone.
To mitigate this risk, administrators must immediately upgrade Drupal Shield to version 1.9.1 or later, where these restrictions have been properly implemented. In environments where upgrading is temporarily unfeasible, compensating controls should be deployed at the web server or reverse proxy level. Implementing rate limiting rules that restrict the number of authentication requests per IP address over a specific timeframe can effectively neutralize brute force attempts. Additionally, enforcing strong password policies and enabling multi-factor authentication adds critical layers of defense that reduce the likelihood of successful credential compromise even if an attacker bypasses other controls. Regular auditing of access logs for anomalous login patterns is also recommended to detect any ongoing exploitation activities.