CVE-2015-0826 in Firefox
Summary
by MITRE
The nsTransformedTextRun::SetCapitalization function in Mozilla Firefox before 36.0 allows remote attackers to execute arbitrary code or cause a denial of service (out-of-bounds read of heap memory) via a crafted Cascading Style Sheets (CSS) token sequence that triggers a restyle or reflow operation.
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Analysis
by VulDB Data Team • 03/10/2022
The vulnerability identified as CVE-2015-0826 represents a critical heap-based buffer overflow in Mozilla Firefox's text rendering engine, specifically within the nsTransformedTextRun::SetCapitalization function. This flaw exists in versions prior to Firefox 36.0 and demonstrates how seemingly benign CSS styling operations can be exploited to achieve remote code execution or denial of service conditions. The vulnerability stems from insufficient input validation and memory boundary checking when processing CSS token sequences that trigger restyle or reflow operations, which are fundamental components of web page rendering.
The technical exploitation of this vulnerability occurs through carefully crafted CSS token sequences that manipulate the capitalization transformation logic within Firefox's rendering pipeline. When the browser processes these malicious CSS inputs, the nsTransformedTextRun::SetCapitalization function fails to properly validate the boundaries of heap memory allocations, leading to an out-of-bounds read condition. This memory corruption can be leveraged by attackers to either execute arbitrary code within the browser's memory space or cause a controlled crash that results in denial of service. The vulnerability specifically targets the browser's text processing capabilities and demonstrates how CSS styling properties can be weaponized to compromise system integrity.
The operational impact of this vulnerability extends beyond simple exploitation as it affects the core rendering functionality of Firefox, making it particularly dangerous in web browsing environments where users encounter untrusted content. Attackers can craft malicious websites or HTML documents containing the specific CSS sequences that trigger this flaw, potentially leading to complete browser compromise without user interaction beyond visiting the malicious site. The vulnerability's classification as a heap-based buffer overflow aligns with CWE-121 and CWE-125, which describe memory safety issues in heap memory operations. This weakness can be mapped to ATT&CK technique T1059.007 for command and script interpreter execution, as successful exploitation could enable attackers to execute arbitrary code within the browser context.
Mitigation strategies for CVE-2015-0826 primarily focus on immediate version updates to Firefox 36.0 or later, where the underlying memory management and input validation issues have been addressed. System administrators should implement comprehensive patch management protocols to ensure all users have the latest security updates installed. Additionally, browser security configurations can be enhanced through content security policy implementations and sandboxing measures that limit the potential impact of such vulnerabilities. The vulnerability highlights the importance of robust input validation in web rendering engines and demonstrates why continuous security auditing of core browser components is essential for maintaining user protection against sophisticated exploitation techniques.