CVE-2006-4570 in Firefox
Summary
by MITRE
Mozilla Thunderbird before 1.5.0.7 and SeaMonkey before 1.0.5, with "Load Images" enabled, allows remote user-assisted attackers to bypass settings that disable JavaScript via a remote XBL file in a message that is loaded when the user views, forwards, or replies to the original message.
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Analysis
by VulDB Data Team • 07/08/2019
This vulnerability exists in Mozilla Thunderbird versions prior to 1.5.0.7 and SeaMonkey versions prior to 1.0.5 where the security mechanism designed to disable JavaScript execution can be bypassed through a remote XBL file. The flaw occurs when the "Load Images" setting is enabled, creating a pathway for attackers to execute malicious code despite user security preferences. The vulnerability specifically targets the message viewing process where remote content is loaded automatically, allowing attackers to embed malicious XBL (XML Binding Language) files within email messages that execute when users interact with the message through viewing, forwarding, or replying operations.
The technical implementation of this vulnerability exploits the way Thunderbird and SeaMonkey handle remote content loading when images are enabled. XBL files are XML-based binding files that can contain JavaScript code and are typically used for creating custom user interface components in Firefox and Thunderbird. When an attacker crafts an email message containing a remote XBL file reference, the client automatically downloads and executes this content when the user performs the specified actions. This bypasses the intended JavaScript security controls because the XBL file is loaded through the normal image loading mechanism rather than being explicitly blocked by the JavaScript disable setting.
The operational impact of this vulnerability is significant as it allows remote attackers to execute arbitrary code on vulnerable systems with the privileges of the user running the email client. This creates a persistent threat vector where attackers can deliver malicious payloads through seemingly benign email messages, potentially leading to complete system compromise. The vulnerability is particularly dangerous because it requires minimal user interaction beyond viewing or replying to the message, making it an effective vector for social engineering attacks. The attack can be executed without any special privileges or complex exploitation techniques, making it accessible to attackers with basic knowledge of web technologies.
This vulnerability aligns with CWE-94, which covers "Improper Control of Generation of Code" and specifically relates to the improper handling of external content that can lead to code execution. The issue also maps to ATT&CK technique T1190, "Exploit Public-Facing Application," as it represents an attack vector through email clients that are commonly exposed to external threats. The security flaw demonstrates a critical design weakness in how the email clients handle cross-domain content loading and validation, particularly in the context of remote XBL file execution. Organizations using affected versions should immediately update to patched versions, disable automatic image loading, and implement additional email filtering measures to reduce exposure. The vulnerability also underscores the importance of proper content security policies and the need for comprehensive sandboxing of external content in email clients to prevent such bypasses of security controls.