CVE-2022-1834 in Thunderbird
Summary
by MITRE • 12/22/2022
When displaying the sender of an email, and the sender name contained the Braille Pattern Blank space character multiple times, Thunderbird would have displayed all the spaces. This could have been used by an attacker to send an email message with the attacker's digital signature, that was shown with an arbitrary sender email address chosen by the attacker. If the sender name started with a false email address, followed by many Braille space characters, the attacker's email address was not visible. Because Thunderbird compared the invisible sender address with the signature's email address, if the signing key or certificate was accepted by Thunderbird, the email was shown as having a valid digital signature. This vulnerability affects Thunderbird < 91.10.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 04/17/2025
This vulnerability in Mozilla Thunderbird represents a sophisticated social engineering attack vector that exploits character encoding and display behavior to manipulate email authenticity verification. The flaw resides in how Thunderbird processes and displays sender names containing Braille Pattern Blank characters, which are invisible Unicode characters that appear as spaces but do not render visibly on screen. When an attacker crafts an email with a sender name that begins with a legitimate email address followed by multiple Braille space characters, the actual sender address becomes obscured in the display interface. This creates a misleading visual representation where the email appears to originate from a trusted source while actually being sent by an attacker who controls the digital signature. The vulnerability specifically impacts versions prior to 91.10 and demonstrates a critical weakness in email client trust verification mechanisms.
The technical implementation of this attack exploits the difference between how email addresses are processed internally versus how they are displayed visually to users. The Braille Pattern Blank character U+2800 is a Unicode control character that renders as a space but is not displayed in the user interface, allowing attackers to manipulate the visual representation of email addresses while maintaining the underlying technical address structure. This creates a scenario where the email client's signature verification system compares the invisible address components with the digital signature's email address, potentially accepting signatures from attackers who control the signing keys. The vulnerability operates at the intersection of user interface rendering and cryptographic verification, where the visual deception bypasses the security checks that should prevent such mismatches. This behavior aligns with CWE-174, which addresses the weakness of insufficient character encoding normalization in security-critical applications.
The operational impact of this vulnerability extends beyond simple phishing attempts to include more sophisticated attacks such as impersonation of trusted contacts, corporate executives, or security personnel. Attackers could craft emails that appear to come from legitimate sources such as IT departments, financial institutions, or executive offices, while maintaining their own digital signatures and controlling the message content. The effectiveness of this attack is enhanced by the fact that users typically rely on visual cues to verify sender authenticity, making the invisible character manipulation particularly dangerous. Email clients that implement similar display mechanisms without proper normalization could be vulnerable to analogous attacks, as the fundamental issue lies in the handling of invisible Unicode characters during address display processing. This vulnerability represents a significant risk to organizations that depend on digital signatures for email authentication and trust verification.
Mitigation strategies for this vulnerability require multiple layers of protection including immediate patching to version 91.10 or later, which implements proper character normalization and display handling for invisible Unicode characters. Organizations should also implement additional email security measures such as domain-based message authentication, reporting, and conformance protocols that can detect and flag suspicious address patterns. Security awareness training should emphasize that visual representations of email addresses may not always reflect the actual technical address structure, particularly when dealing with unusual character sequences. System administrators should consider implementing email filtering rules that can identify and quarantine messages containing excessive invisible character sequences, and organizations should review their digital signature policies to ensure that signature verification does not rely solely on visual address matching. The vulnerability underscores the importance of proper input validation and character handling in security-critical applications, as outlined in the ATT&CK framework's techniques for privilege escalation and credential access through social engineering.