CVE-2014-2018 in Thunderbird
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Mozilla Thunderbird 17.x through 17.0.8, Thunderbird ESR 17.x through 17.0.10, and SeaMonkey before 2.20 allows user-assisted remote attackers to inject arbitrary web script or HTML via an e-mail message containing a data: URL in a (1) OBJECT or (2) EMBED element, a related issue to CVE-2013-6674.
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Analysis
by VulDB Data Team • 04/23/2025
This cross-site scripting vulnerability exists in Mozilla Thunderbird and SeaMonkey email clients, specifically affecting versions through 17.0.8 and 17.0.10 respectively, with SeaMonkey being vulnerable before version 2.20. The flaw allows remote attackers to execute malicious code through email messages containing specially crafted data: URLs within OBJECT or EMBED HTML elements, creating a user-assisted attack vector where victims must open the malicious email for exploitation to occur. The vulnerability represents a significant security risk as it enables attackers to bypass traditional email security measures and execute arbitrary scripts in the context of the email client's security boundaries, potentially leading to data theft, session hijacking, or further system compromise.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization of HTML content within email messages. When Thunderbird processes email content containing data: URLs within OBJECT or EMBED elements, it fails to properly sanitize or escape these potentially malicious inputs before rendering them in the email display area. This allows attackers to embed malicious JavaScript code or HTML content that executes when the victim opens the email, creating a persistent cross-site scripting attack vector. The vulnerability is categorized as CWE-79 - Improper Neutralization of Input During Web Page Generation, specifically manifesting as a reflected XSS attack pattern. The attack chain requires the victim to open the malicious email, making it a user-assisted rather than fully autonomous exploit, but still poses significant risk in targeted or social engineering attacks.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including credential theft through session cookie harvesting, phishing attacks that appear legitimate within the email client interface, and potentially full system compromise if the email client has elevated privileges or if additional vulnerabilities exist. Attackers can craft emails that appear to come from trusted sources, leveraging the trust relationship between email clients and their users to bypass security controls. The vulnerability affects both regular Thunderbird releases and the Extended Support Release (ESR) versions, indicating it was a widespread issue affecting enterprise email clients that typically require longer support cycles. This makes it particularly concerning for organizations that rely on ESR versions for stability and security continuity.
Mitigation strategies for this vulnerability include immediate patching of affected versions to the latest available releases, implementing email filtering rules to block data: URLs within email content, and educating users about the risks of opening suspicious emails. Organizations should also consider deploying additional security layers such as email gateway filtering, content inspection systems, and web application firewalls to detect and prevent exploitation attempts. Security teams should monitor for indicators of compromise including unusual email traffic patterns or attempts to access data: URLs in email content. The ATT&CK framework categorizes this as a technique involving credential access through social engineering and web application attacks, with potential for privilege escalation if the email client has elevated system permissions. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other email clients and web applications, as this vulnerability demonstrates how HTML rendering flaws in email clients can create persistent attack surfaces.