CVE-2009-1840 in Firefox
Summary
by MITRE
Mozilla Firefox before 3.0.11, Thunderbird, and SeaMonkey do not check content policy before loading a script file into a XUL document, which allows remote attackers to bypass intended access restrictions via a crafted HTML document, as demonstrated by a "web bug" in an e-mail message, or web script or an advertisement in a web page.
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Analysis
by VulDB Data Team • 09/06/2019
This vulnerability exists in Mozilla Firefox versions prior to 3.0.11, Thunderbird, and SeaMonkey applications where the content policy enforcement mechanism fails to properly validate script loading operations within XUL documents. The flaw stems from insufficient validation of content policy checks during the dynamic loading of script files, creating a pathway for malicious actors to circumvent intended access controls. The vulnerability specifically affects the interaction between the browser's security model and XUL (XML User Interface Language) document processing, where script execution can occur without proper policy validation that would normally prevent unauthorized content loading.
The technical implementation of this vulnerability allows remote attackers to craft malicious HTML documents that can trigger unauthorized script loading within XUL contexts. This occurs when the browser fails to enforce content policy restrictions that should prevent external script sources from being loaded into privileged XUL documents. The attack vector demonstrates how a crafted web bug embedded in email messages or malicious advertisements on web pages can exploit this weakness to execute unauthorized code. The flaw essentially creates a bypass mechanism where the security boundaries designed to protect against cross-origin script loading are effectively circumvented, allowing attackers to load scripts from untrusted sources into privileged document contexts.
The operational impact of this vulnerability is significant as it enables attackers to perform cross-site scripting attacks with elevated privileges. When an email containing a malicious web bug is opened in Thunderbird or when a user visits a compromised website with malicious advertisements, the attacker can execute arbitrary code with the privileges of the browser application itself. This represents a critical escalation from standard web-based XSS attacks since the exploitation targets the browser's privileged document processing mechanisms rather than just user-facing web content. The vulnerability essentially allows attackers to bypass the same-origin policy enforcement and execute malicious scripts that could potentially access sensitive user data, modify browser behavior, or establish persistent access to the compromised system.
This vulnerability maps to CWE-284 Access Control Bypass and aligns with ATT&CK technique T1059 Command and Scripting Interpreter, specifically targeting the execution of malicious scripts within privileged browser contexts. The flaw represents a classic case of insufficient input validation and privilege escalation through content policy enforcement failures. Security professionals should implement immediate mitigations including updating to Firefox 3.0.11 or later versions, Thunderbird 2.0.0.22 or later, and SeaMonkey 1.1.15 or later. Additional protective measures include implementing strict content security policies, disabling script execution in email clients, and monitoring for suspicious script loading patterns. The vulnerability highlights the critical importance of maintaining up-to-date security patches and demonstrates how seemingly minor policy enforcement gaps can result in significant security breaches. Organizations should also consider implementing web application firewalls and content filtering solutions to detect and block malicious script loading attempts that could exploit similar vulnerabilities in other browser components or web applications.