CVE-2013-0748 in Firefox
Summary
by MITRE
The XBL.__proto__.toString implementation in Mozilla Firefox before 18.0, Firefox ESR 10.x before 10.0.12 and 17.x before 17.0.2, Thunderbird before 17.0.2, Thunderbird ESR 10.x before 10.0.12 and 17.x before 17.0.2, and SeaMonkey before 2.15 makes it easier for remote attackers to bypass the ASLR protection mechanism by calling the toString function of an XBL object.
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Analysis
by VulDB Data Team • 04/20/2021
The vulnerability described in CVE-2013-0748 represents a critical information disclosure flaw affecting Mozilla Firefox and related applications including Thunderbird and SeaMonkey. This issue specifically targets the XBL._proto_.toString implementation within the browser's JavaScript engine, creating a pathway for remote attackers to circumvent operating system security mechanisms. The flaw exists in versions prior to Firefox 18.0, Firefox ESR 10.x before 10.0.12, 17.x before 17.0.2, Thunderbird 17.0.2, Thunderbird ESR 10.x before 10.0.12, 17.x before 17.0.2, and SeaMonkey 2.15. The vulnerability stems from improper handling of the toString method when invoked on XBL (XML Binding Language) objects, which are used to extend HTML elements with custom behavior in Firefox's rendering engine.
The technical exploitation of this vulnerability relies on the ability to predict memory addresses through information leakage mechanisms. When the toString function is called on an XBL object, it inadvertently reveals memory layout information that can be used to defeat Address Space Layout Randomization, a fundamental security feature designed to prevent exploitation of memory corruption vulnerabilities. This occurs because the XBL implementation does not properly sanitize or restrict the information exposed through the toString method, allowing attackers to extract address pointers that would normally be randomized during system operation. The flaw operates at the intersection of JavaScript execution and memory management, leveraging the browser's internal object model to expose sensitive information.
The operational impact of this vulnerability is significant as it enables attackers to bypass one of the primary defenses against exploitation of other security flaws. ASLR bypass allows adversaries to more effectively target memory corruption vulnerabilities such as buffer overflows or use-after-free conditions that might otherwise be difficult to exploit due to randomized memory layouts. This vulnerability essentially provides a stepping stone for more sophisticated attacks, making it particularly dangerous in environments where users may be targeted by advanced persistent threats. The attack vector is remote and can be executed through malicious web content, making it accessible to attackers without requiring physical access to the target system.
Security mitigations for this vulnerability primarily involve upgrading to the patched versions of the affected software products. Mozilla released updates for Firefox 18.0, Thunderbird 17.0.2, and SeaMonkey 2.15, which address the XBL.toString implementation issue. Organizations should implement immediate patch management procedures to ensure all affected systems are updated. Additionally, browser hardening practices such as enabling sandboxing features, disabling unnecessary JavaScript functionality, and implementing content security policies can provide additional defense in depth. This vulnerability aligns with CWE-200 (Information Exposure) and can be categorized under ATT&CK technique T1059.007 (Command and Scripting Interpreter: JavaScript) when used as part of multi-stage attack chains. The flaw demonstrates the importance of proper object model implementation in security-sensitive applications and highlights the need for comprehensive testing of edge cases in JavaScript engine implementations.