CVE-2018-18655 in Prayer List Module
Summary
by MITRE
Prayer through 1.3.5 sends a Referer header, containing a user's username, when a user clicks on a link in their email because header.t lacks a no-referrer setting.
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Analysis
by VulDB Data Team • 04/06/2020
The vulnerability identified as CVE-2018-18655 resides within the Prayer email client version 1.3.5 and represents a significant privacy and security flaw related to HTTP header handling. This issue manifests when users interact with links embedded in their email messages, creating an unintended information disclosure mechanism that compromises user anonymity and potentially exposes sensitive authentication data.
The technical flaw stems from the application's improper handling of HTTP Referer headers during web navigation initiated from email content. When a user clicks on a hyperlink within an email message, the Prayer client automatically includes the user's username within the Referer header field, effectively transmitting this identifying information to external web servers. This behavior violates fundamental security principles regarding information minimization and user privacy protection during web browsing activities.
The operational impact of this vulnerability extends beyond simple information disclosure, creating potential attack vectors for malicious actors who can harvest user credentials and authentication details. The Referer header typically contains the URL of the previous page, but in this case, the inclusion of the username creates a direct correlation between the user's identity and their browsing activity. This exposure can be exploited in various attack scenarios including credential harvesting, session hijacking, and targeted phishing campaigns that leverage the disclosed authentication information.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-200, which addresses "Information Exposure," and represents a clear violation of the principle of least privilege in information sharing. The flaw also intersects with ATT&CK technique T1566, "Phishing," as it enables more sophisticated phishing attacks by providing attackers with additional user identification information. Additionally, this issue relates to CWE-384, "Session Management Flaws," as it compromises the integrity of user session information through unintended disclosure of authentication tokens or identifiers.
The vulnerability demonstrates poor security implementation practices in the application's HTTP header management system, specifically lacking proper sanitization or filtering of sensitive information before transmission. The absence of a no-referrer setting in the header.t configuration file represents a fundamental security oversight that exposes users to unnecessary risk during routine email interaction activities. This flaw essentially transforms legitimate email navigation into a potential data exfiltration channel, making it particularly concerning for users who rely on email clients for sensitive communications.
Mitigation strategies should focus on immediate patching of the application to implement proper header handling with appropriate no-referrer directives. Organizations should also consider implementing network-level controls to monitor and filter Referer header content, particularly when it contains user identification information. Additionally, user education regarding the risks of clicking links in email messages remains critical, though this approach addresses symptoms rather than the underlying vulnerability. The fix should ensure that all outgoing HTTP requests maintain user privacy by default, with explicit configuration required for any intentional disclosure of referral information.