CVE-2018-1081 in Moodle
Summary
by MITRE
A flaw was found in Moodle 3.4 to 3.4.1, 3.3 to 3.3.4, 3.2 to 3.2.7, 3.1 to 3.1.10 and earlier unsupported versions. Unauthenticated users can trigger custom messages to admin via paypal enrol script. Paypal IPN callback script should only send error emails to admin after request origin was verified, otherwise admin email can be spammed.
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Analysis
by VulDB Data Team • 02/08/2021
This vulnerability exists in Moodle versions ranging from 3.4.0 to 3.4.1, 3.3.0 to 3.3.4, 3.2.0 to 3.2.7, 3.1.0 to 3.1.10, and earlier unsupported versions. The flaw resides in the paypal enrol script's handling of instant payment notification (IPN) callbacks from PayPal's payment processing system. When unauthenticated users send malicious IPN requests to the Moodle system, the paypal enrol script fails to properly verify the request origin before sending error notifications to administrators. This design flaw creates a condition where any external party can trigger automated email notifications to system administrators without authentication or authorization, leading to potential spamming of administrative email accounts. The vulnerability stems from inadequate input validation and origin verification mechanisms within the payment processing callback handler, which should have implemented proper security checks before generating administrative alerts. According to CWE-284, this represents an access control weakness where insufficient verification of request sources allows unauthorized entities to perform privileged actions. The issue directly relates to ATT&CK technique T1190 which involves exploiting vulnerabilities in web applications to gain unauthorized access or execute malicious actions.
The technical implementation of this vulnerability involves the paypal enrol script's IPN callback handler failing to validate incoming requests against known PayPal IP addresses or verify the authenticity of payment notifications. When PayPal sends an IPN message to Moodle's payment processing endpoint, the system should verify that the request originates from PayPal's official servers before triggering any administrative notifications. Without this verification step, any user capable of sending HTTP requests to the Moodle system can generate error emails by crafting malicious IPN payloads. The script's error handling mechanism is designed to alert administrators about processing failures, but this mechanism lacks proper access controls and request validation. The vulnerability essentially creates a denial of service condition for administrators through email spamming, while also potentially exposing sensitive information about the system's payment processing capabilities. The flaw demonstrates poor security architecture where the system assumes all incoming requests are legitimate without proper authentication or source verification.
The operational impact of this vulnerability extends beyond simple email spamming to potentially compromise system security and administrative efficiency. Administrators may receive overwhelming volumes of spam emails that could obscure legitimate security alerts or system notifications, creating a situation where critical messages might be missed or ignored. The vulnerability also exposes potential reconnaissance opportunities for attackers who could use this mechanism to identify active Moodle installations or gather information about the system's payment processing infrastructure. This flaw could facilitate further attacks by allowing malicious actors to establish a baseline for system behavior or by overwhelming administrative communication channels. The vulnerability affects organizations that rely on Moodle for educational or training purposes, where payment processing is integrated into course enrollment systems. Attackers could exploit this weakness to disrupt service availability or to perform reconnaissance activities that might lead to more serious security breaches.
Organizations using affected Moodle versions should immediately apply the security patches released by Moodle developers to address this vulnerability. The recommended mitigation includes implementing proper IP address validation for incoming IPN requests and ensuring that all administrative notifications are only triggered after successful verification of request origins. System administrators should also configure proper rate limiting or throttling mechanisms to prevent abuse of the email notification system. Additional security measures include monitoring for unusual patterns in payment processing activity and implementing network-level controls to restrict access to payment processing endpoints. The vulnerability highlights the importance of validating all external inputs and implementing defense-in-depth strategies for web application security. Organizations should conduct regular security assessments of their learning management systems to identify similar vulnerabilities that could compromise system integrity or availability. This issue serves as a reminder of the critical need for proper access control implementation in payment processing systems and the importance of verifying all incoming requests before triggering administrative actions.