CVE-2019-3850 in Moodle
Summary
by MITRE
A vulnerability was found in moodle before versions 3.6.3, 3.5.5, 3.4.8 and 3.1.17. Links within assignment submission comments would open directly (in the same window). Although links themselves may be valid, opening within the same window and without the no-referrer header policy made them more susceptible to exploits.
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Analysis
by VulDB Data Team • 09/08/2025
The vulnerability identified as CVE-2019-3850 represents a significant security flaw in the Moodle learning management system that affected multiple versions prior to 3.6.3, 3.5.5, 3.4.8, and 3.1.17. This issue stems from improper handling of hyperlinks within assignment submission comments, creating an exploitable condition that could be leveraged by malicious actors to conduct various cyber attacks. The flaw specifically relates to the browser behavior when users click on links embedded within comment fields, which would automatically open in the same browser window without appropriate security headers.
The technical implementation of this vulnerability involves the absence of proper security measures when rendering hyperlinks within Moodle's assignment submission interface. When users submit comments containing links, the system fails to implement the no-referrer header policy that would normally prevent the transmission of referral information when navigating away from the current page. This lack of security enforcement creates a potential vector for cross-site scripting attacks and phishing attempts, as the target page can potentially access the referring page's context through the referrer header. The vulnerability directly maps to CWE-611, which addresses improper access control in web applications, and specifically relates to the insecure handling of user-provided content that could be manipulated to execute malicious actions.
The operational impact of this vulnerability extends beyond simple navigation behavior, as it creates opportunities for attackers to exploit user trust and manipulate browser sessions. When links open in the same window without proper security headers, it enables potential attackers to craft malicious URLs that could steal session cookies, redirect users to fraudulent sites, or perform unauthorized actions on behalf of the user. The risk is particularly elevated in educational environments where users may be less security-aware and more likely to click on seemingly legitimate links within assignment comments. This vulnerability aligns with ATT&CK technique T1566, which covers social engineering through spearphishing, as the attack vector leverages the trust users place in legitimate assignment comments.
The security implications of this vulnerability are compounded by the fact that Moodle is widely used in educational institutions, making it an attractive target for cybercriminals seeking to exploit the trust relationships inherent in academic environments. The lack of proper security headers creates a pathway for attackers to potentially harvest sensitive information or redirect users to malicious sites that could compromise the entire educational platform. Organizations using affected Moodle versions face significant risk of credential theft, session hijacking, and potential data breaches through this seemingly minor implementation flaw. The vulnerability demonstrates how basic security practices, such as implementing proper HTTP headers and link handling policies, can prevent sophisticated attacks that might otherwise go undetected in less secure environments.