CVE-2016-5276 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the mozilla::a11y::DocAccessible::ProcessInvalidationList function in Mozilla Firefox before 49.0 and Firefox ESR 45.x before 45.4 allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via an aria-owns attribute.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability CVE-2016-5276 represents a critical use-after-free flaw within Mozilla Firefox's accessibility subsystem, specifically in the DocAccessible::ProcessInvalidationList function. This issue affects Firefox versions prior to 49.0 and Firefox ESR 45.x versions prior to 45.4, creating a significant security risk for users operating these outdated browser versions. The vulnerability stems from improper memory management when processing accessibility attributes, particularly the aria-owns attribute which is part of the accessibility infrastructure defined by wai-aria specifications.
The technical exploitation of this vulnerability occurs through a carefully crafted aria-owns attribute that triggers a use-after-free condition in the accessibility tree processing code. When Firefox encounters such malformed accessibility attributes, the DocAccessible::ProcessInvalidationList function fails to properly manage memory references, leading to heap memory corruption. This memory corruption can be leveraged by remote attackers to execute arbitrary code with the privileges of the browser process or to cause a denial of service through application crashes. The vulnerability is classified as CWE-416, which specifically addresses use-after-free conditions, and aligns with ATT&CK technique T1059.007 for remote code execution through browser exploitation.
The operational impact of this vulnerability extends beyond simple exploitation as it affects the fundamental accessibility features of Firefox, potentially compromising the security of users who rely on assistive technologies. Attackers can craft malicious web pages that include crafted aria-owns attributes to trigger the vulnerability, making this a serious concern for web content that may be processed through Firefox's accessibility engine. The heap corruption can manifest in various ways including application crashes, memory corruption that may lead to code execution, or complete browser instability. This vulnerability particularly affects users who have accessibility features enabled in Firefox, as the exploitation path specifically targets the accessibility processing code paths.
Mitigation strategies for CVE-2016-5276 primarily focus on immediate version updates to Firefox 49.0 or Firefox ESR 45.4 and later, which contain the necessary patches to address the memory management issues in the DocAccessible::ProcessInvalidationList function. Organizations should implement comprehensive patch management processes to ensure all Firefox installations are updated promptly, as this vulnerability is actively exploited in the wild. Additionally, security teams should monitor for any attempts to exploit this vulnerability through web content and consider implementing web application firewalls or content filtering solutions that can detect and block malicious aria-owns attributes. The fix implemented by Mozilla addresses the root cause by properly managing memory references and ensuring that freed memory is not accessed again during accessibility tree processing operations, thereby preventing the use-after-free condition that enabled remote code execution.