CVE-2017-7829 in Thunderbird
Summary
by MITRE
It is possible to spoof the sender's email address and display an arbitrary sender address to the email recipient. The real sender's address is not displayed if preceded by a null character in the display string. This vulnerability affects Thunderbird < 52.5.2.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability in Mozilla Thunderbird represents a sophisticated email spoofing mechanism that exploits the email client's handling of display names and sender addresses. The flaw allows attackers to manipulate how email addresses appear to recipients by leveraging null character injection techniques within the display string of email headers. When a null character precedes the real sender's address in the display name field, the email client fails to properly render the authentic sender information, instead showing a crafted or arbitrary sender address. This creates a deceptive environment where recipients may be misled about the true origin of emails, potentially enabling phishing attacks, social engineering campaigns, or malicious communication attempts. The vulnerability specifically impacts Thunderbird versions prior to 52.5.2, indicating that the issue was addressed through proper input validation and sanitization of email header fields.
The technical implementation of this vulnerability stems from insufficient validation of display name fields in email headers, where the client processes the display string without adequate sanitization of special characters including null bytes. This weakness falls under the category of improper input validation, which aligns with CWE-20 - Improper Input Validation, and more specifically relates to CWE-116 - Improper Encoding or Escaping of Output. The vulnerability demonstrates how character encoding issues in email client implementations can create security flaws that affect the integrity of email authentication and trust mechanisms. When a null character is embedded in the display name, it effectively terminates string processing, causing the client to ignore subsequent characters including legitimate sender information.
The operational impact of this vulnerability extends beyond simple email deception, potentially enabling sophisticated attack vectors that leverage user trust in email communications. Attackers can craft emails that appear to originate from legitimate sources such as financial institutions, colleagues, or known contacts, making phishing attempts more convincing and potentially leading to successful credential theft, financial fraud, or data breaches. The vulnerability particularly affects users who rely on Thunderbird for business or personal communications, as it undermines the fundamental security assumption that email headers can be trusted to accurately represent sender information. This flaw can be exploited in targeted attacks where attackers have knowledge of the victim's email environment and can craft convincing spoofed messages.
Mitigation strategies for this vulnerability involve immediate patching of Thunderbird installations to version 52.5.2 or later, which includes proper handling of null characters in display names and enhanced validation of email header fields. Organizations should implement comprehensive email security measures including email authentication protocols such as SPF, DKIM, and DMARC to provide additional layers of protection against spoofing attacks. Security teams should also conduct regular security awareness training to educate users about recognizing potentially spoofed emails and the importance of verifying sender authenticity through multiple channels. The fix implemented by Mozilla addresses the root cause by ensuring that null characters and other special characters are properly handled during display name processing, preventing the truncation of legitimate sender information. This vulnerability highlights the importance of robust input validation in email client software and demonstrates how seemingly minor implementation flaws can have significant security implications in communication systems.