CVE-2018-5185 in Thunderbird
Summary
by MITRE
Plaintext of decrypted emails can leak through by user submitting an embedded form. This vulnerability affects Thunderbird ESR < 52.8 and Thunderbird < 52.8.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability represents a critical information disclosure flaw in Mozilla Thunderbird email clients that allows plaintext email content to be inadvertently exposed through user interaction with embedded forms. The issue specifically impacts Thunderbird ESR versions prior to 52.8 and standard Thunderbird versions before 52.8, creating a significant security risk for users who may unknowingly trigger the vulnerability while processing legitimate email communications. The flaw occurs when users interact with embedded forms contained within decrypted email messages, potentially exposing sensitive plaintext content that should remain protected within the encrypted email environment.
The technical mechanism behind this vulnerability involves the improper handling of form elements within decrypted email content, where the email client fails to adequately sanitize or isolate form submissions from the surrounding plaintext email data. When users submit forms embedded within email messages, the client may inadvertently expose the underlying plaintext content through various channels including form action URLs, hidden form fields, or other submission mechanisms that can carry the decrypted email text. This represents a classic case of insufficient input validation and output sanitization, where the application fails to properly separate user-controllable form data from sensitive email content. The vulnerability aligns with CWE-20, which addresses improper input validation, and CWE-79, which covers cross-site scripting vulnerabilities where user-controllable data can be injected into web applications.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks including credential theft, session hijacking, and data exfiltration. Attackers could craft malicious emails containing embedded forms that, when submitted by unsuspecting users, would transmit plaintext email content to attacker-controlled servers. This creates a vector for targeted attacks against users who handle sensitive communications, particularly in enterprise environments where email encryption is commonly used to protect confidential information. The vulnerability affects users who regularly process encrypted emails, making it particularly dangerous in contexts where financial, medical, or proprietary information is transmitted through email channels. Organizations that rely on Thunderbird for secure email communications face significant risk exposure, as this vulnerability can be exploited without requiring any special privileges or advanced technical skills from attackers.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected Thunderbird installations to version 52.8 or later, which includes the necessary code modifications to properly isolate form submissions from plaintext email content. System administrators should implement comprehensive email security policies that include user education about the risks of interacting with embedded forms in email messages, particularly those that appear to be from untrusted sources. Network security controls such as email filtering and content inspection systems can help detect and block suspicious email content that may contain embedded forms designed to exploit this vulnerability. Organizations should also consider implementing additional layers of protection including email encryption policies that require specific security measures for sensitive communications, and monitoring systems that can detect unusual form submission patterns from email clients. The remediation process should include thorough testing of patched versions to ensure that the fix does not introduce regressions in email functionality while maintaining the security improvements. This vulnerability demonstrates the importance of proper input sanitization and output encoding in web applications and email clients, aligning with ATT&CK technique T1190 for exploit public-facing applications and T1059 for command and scripting interpreters, as attackers could potentially leverage this vulnerability to execute further malicious activities through compromised email systems.