CVE-2012-4142 in Web Browser
Summary
by MITRE
Opera before 12.01 on Windows and UNIX, and before 11.66 and 12.x before 12.01 on Mac OS X, ignores some characters in HTML documents in unspecified circumstances, which makes it easier for remote attackers to conduct cross-site scripting (XSS) attacks via a crafted document.
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Analysis
by VulDB Data Team • 04/22/2019
The vulnerability identified as CVE-2012-4142 represents a critical security flaw in the Opera web browser across multiple platforms including Windows, UNIX, and Mac OS X. This issue stems from Opera's improper handling of certain characters within HTML documents, creating a condition that significantly weakens the browser's security mechanisms. The flaw specifically affects Opera versions prior to 11.66 for Mac OS X and versions before 12.01 for both Windows and UNIX platforms, making it a widespread concern across the browser's user base during that period. The vulnerability's classification aligns with CWE-79, which addresses Cross-Site Scripting flaws, and demonstrates how character encoding issues can create exploitable conditions in web browsers.
The technical nature of this vulnerability involves Opera's HTML parser failing to properly process or reject certain characters in HTML documents under unspecified circumstances. This character handling inconsistency creates a window of opportunity for attackers to craft malicious HTML documents that bypass the browser's security controls. When Opera encounters these specially crafted documents, it fails to properly sanitize or interpret the embedded characters, allowing potentially malicious content to be executed in the context of the user's browsing session. This behavior fundamentally undermines the browser's ability to distinguish between legitimate and malicious HTML content, particularly in scenarios involving cross-site scripting attacks where attackers seek to inject client-side scripts.
The operational impact of this vulnerability is severe and directly enables remote attackers to conduct cross-site scripting attacks with significantly reduced difficulty. Attackers can exploit this flaw by creating HTML documents that contain specially crafted character sequences, which Opera's parser fails to properly handle. This allows malicious scripts to execute in the context of the victim's session, potentially leading to session hijacking, data theft, or further exploitation of the victim's browser environment. The vulnerability essentially weakens Opera's security boundaries, making it easier for attackers to bypass the browser's built-in protections and execute malicious code without requiring additional privileges or complex attack vectors.
The security implications extend beyond simple XSS exploitation, as this vulnerability demonstrates how seemingly minor character handling issues can create significant security weaknesses in web browsers. The flaw's presence across multiple operating systems indicates a fundamental issue in Opera's HTML parsing implementation that affects a broad user base. Organizations and individuals using affected Opera versions face increased risk of targeted attacks, particularly in environments where users may encounter untrusted web content. This vulnerability highlights the importance of comprehensive input validation and proper character encoding handling in web browser implementations, as even subtle parsing inconsistencies can create exploitable conditions that align with ATT&CK technique T1211 for exploitation of browser vulnerabilities.
Mitigation strategies for this vulnerability require immediate browser updates to versions that address the character handling issues in Opera's HTML parser. Users should upgrade to Opera 11.66 for Mac OS X and Opera 12.01 for Windows and UNIX platforms to eliminate the risk. Additionally, system administrators should implement browser security policies that enforce regular updates and monitor for vulnerable browser installations. Organizations should consider implementing web application firewalls or content filtering solutions as additional protective measures while ensuring all Opera installations are updated. The fix implemented by Opera addressed the specific character handling inconsistencies in the HTML parser, restoring proper validation of HTML content and eliminating the conditions that allowed XSS attacks to succeed.