CVE-2016-5013 in Moodle
Summary
by MITRE
In Moodle 2.x and 3.x, text injection can occur in email headers, potentially leading to outbound spam.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2016-5013 represents a critical text injection flaw within the Moodle learning management system affecting versions 2.x and 3.x. This security weakness resides in the email header processing functionality where user-supplied input is not properly sanitized before being incorporated into email headers. The flaw allows malicious actors to inject arbitrary text into email headers, which can be exploited to manipulate email routing, spoof sender information, or facilitate spam distribution. The vulnerability stems from inadequate input validation and sanitization mechanisms within the email handling components of Moodle's core architecture.
The technical implementation of this vulnerability exploits the way Moodle processes user-generated content when constructing email headers for various communication functions within the platform. When users create content such as course descriptions, forum posts, or personal messages that contain specially crafted malicious input, this data can be inadvertently included in email header fields without proper filtering. The injection occurs at the point where Moodle concatenates user input with email header construction logic, creating an environment where attacker-controlled text can be embedded within the header structure. This type of vulnerability maps directly to CWE-116, which addresses the improper encoding or escaping of output, and falls under the broader category of injection flaws that compromise system integrity.
The operational impact of CVE-2016-5013 extends beyond simple spam distribution, as it can enable more sophisticated attack vectors within the Moodle ecosystem. Attackers can leverage this vulnerability to send emails that appear to originate from legitimate Moodle sources, potentially leading to phishing campaigns or social engineering attacks that exploit the trust associated with official communications. The vulnerability also creates opportunities for bypassing spam filters and email security measures that rely on header validation, as the injected content can manipulate routing decisions or authentication mechanisms. Additionally, this flaw can be used to disrupt normal email communications within educational institutions, potentially causing legitimate emails to be filtered or rejected by email servers that detect suspicious header content.
Organizations utilizing Moodle platforms should implement immediate mitigations including comprehensive input validation for all user-generated content that may be used in email contexts, implementing strict sanitization routines for email header construction, and deploying monitoring systems to detect anomalous email header patterns. The recommended approach involves updating to patched versions of Moodle where the vulnerability has been addressed through proper input sanitization and validation controls. Security measures should also include implementing email header inspection mechanisms that can identify and block suspicious injection patterns, as well as establishing network-level controls that monitor outbound email traffic for indicators of compromise. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving email spoofing and command and control communications, making it a significant concern for organizations seeking to maintain secure educational communication platforms. The remediation process should also include comprehensive security testing of email functionality and user input handling to prevent similar vulnerabilities from emerging in other components of the system.