CVE-2026-85586 in phpMyFAQ
Summary
by MITRE • 09/04/2026
phpMyFAQ versions before 4.1.8 fail to validate CAPTCHA when the store parameter is set to 'now' in question submission requests. Unauthenticated attackers can bypass CAPTCHA protection and submit unlimited questions directly, causing database pollution and triggering outgoing mail notifications.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in phpMyFAQ versions prior to 4.1.8 represents a critical authentication bypass flaw within the application's user interaction layer. Specifically, this security defect resides in the mechanism handling question submission requests where the store parameter is configured with the value 'now'. In standard web application security models, CAPTCHA challenges are deployed as anti-automation controls to distinguish human users from automated scripts or malicious bots. The intended behavior requires that any request attempting to submit a new FAQ entry must first successfully validate against this challenge token. However, due to insufficient input validation logic within the backend processing routine for this specific parameter state, the application fails to enforce the CAPTCHA verification step entirely when the store mode is set to immediate submission. This oversight creates a direct path for unauthenticated actors to circumvent one of the primary defenses against automated abuse and denial-of-service attacks targeting user-generated content systems.
From a technical perspective, the root cause lies in the conditional logic governing the validation sequence during request processing. When an HTTP POST or GET request is received with the store parameter explicitly set to 'now', the application's security middleware skips the execution of the CAPTCHA verification module. This allows any client, regardless of whether they possess valid session credentials or have solved a cryptographic challenge, to inject arbitrary data into the system. The flaw effectively neutralizes the anti-bot protection designed to limit request rates and ensure human intent behind content creation. By exploiting this logic gap, an attacker can programmatically generate thousands of submission requests in rapid succession without encountering any blocking mechanisms or verification prompts that would normally interrupt such automated behavior.
The operational impact of this vulnerability is severe, primarily manifesting as database pollution and potential service degradation through resource exhaustion. Since attackers can submit unlimited questions directly, the underlying database will be flooded with potentially malicious, spammy, or nonsensical entries. This not only degrades the quality and usability of the FAQ knowledge base but also increases storage overhead and query load on the database server. Furthermore, each successful submission triggers outgoing mail notifications to administrators or designated recipients as per standard configuration settings. An attacker can leverage this feature to conduct a low-cost denial-of-service attack by flooding email inboxes with thousands of automated messages, potentially causing mailbox quota exhaustion for system owners and increasing infrastructure costs associated with email relay services. This behavior aligns closely with CWE-798, which describes the use of hardcoded or default credentials that allow unauthorized access, although in this context it extends to a logic flaw allowing unauthenticated action execution akin to CWE-20 Improper Input Validation.
In terms of threat modeling and adversary tactics, this vulnerability facilitates actions consistent with MITRE ATT&CK technique T1190 Exploit Public-Facing Application. The attacker leverages the exposed web interface to inject content without authentication, which can serve as a foothold for further malicious activities such as defacement or phishing if the submitted questions contain harmful links or social engineering payloads. Additionally, the ability to trigger mass email notifications relates to T1498 Network Denial of Service, specifically through resource exhaustion via application-layer flooding. The lack of rate limiting in conjunction with the CAPTCHA bypass makes this a high-risk vector for automated abuse campaigns targeting public-facing knowledge bases that rely on user contributions.
To mitigate this vulnerability and restore security integrity, immediate patching to phpMyFAQ version 4.1.8 or later is required as it addresses the validation logic error. For environments where an upgrade is not immediately feasible, several compensating controls should be implemented at the network or application level. Web Application Firewalls can be configured with rulesets that detect and block abnormal volumes of submission requests from single IP addresses, effectively mitigating the impact of automated flooding even if the CAPTCHA bypass succeeds. Additionally, implementing strict rate limiting on the question submission endpoint is crucial to prevent resource exhaustion regardless of authentication status. Administrators should also review email notification configurations to ensure they do not trigger for every single submission without throttling mechanisms in place, thereby reducing the potential damage from spam-based denial-of-service attacks while awaiting a permanent code fix.