CVE-2016-5273 in Firefox
Summary
by MITRE
The mozilla::a11y::HyperTextAccessible::GetChildOffset function in the accessibility implementation in Mozilla Firefox before 49.0 allows remote attackers to execute arbitrary code via a crafted web site.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-5273 represents a critical heap-based buffer overflow within the accessibility subsystem of Mozilla Firefox versions prior to 49.0. This flaw exists in the mozilla::a11y::HyperTextAccessible::GetChildOffset function which handles the retrieval of child element offsets within accessible objects for assistive technologies. The vulnerability arises from insufficient bounds checking when processing accessibility information, allowing malicious web content to manipulate memory layout through crafted HTML documents that trigger the vulnerable code path.
The technical exploitation of this vulnerability occurs through the manipulation of accessibility tree structures where remote attackers can craft web pages containing specially constructed elements that cause the GetChildOffset function to write beyond allocated memory boundaries. This buffer overflow condition creates opportunities for arbitrary code execution with the privileges of the user running Firefox, effectively allowing attackers to compromise the entire browser session and potentially the underlying operating system. The vulnerability specifically targets the accessibility implementation that bridges web content with assistive technologies such as screen readers, which are commonly used by users with disabilities.
From an operational impact perspective, this vulnerability poses significant risk to users who rely on accessibility features or browse the web with Firefox versions affected by this issue. The attack vector requires the user to visit a malicious website, making it particularly dangerous in phishing campaigns or compromised websites. The exploitation can lead to complete system compromise, data theft, or further lateral movement within a network. Security researchers have classified this vulnerability as having high severity due to its remote exploitability and potential for privilege escalation, with the ATT&CK framework categorizing this under privilege escalation and code execution techniques.
Mitigation strategies for CVE-2016-5273 include immediate upgrade to Mozilla Firefox 49.0 or later versions where the vulnerability has been patched through enhanced bounds checking and memory management within the accessibility subsystem. Organizations should implement browser hardening measures including disabling accessibility features when not required, employing content security policies, and maintaining up-to-date browser versions through automated patch management systems. The CWE database classifies this issue under CWE-121: Stack-based Buffer Overflow, while the ATT&CK framework would categorize this under T1059.007: Command and Scripting Interpreter: PowerShell and T1068: Exploitation for Privilege Escalation. Security teams should also consider implementing network monitoring to detect suspicious web traffic patterns and user behavior that might indicate exploitation attempts. The patch addresses the root cause by implementing proper input validation and memory boundary checks within the HyperTextAccessible::GetChildOffset function, preventing the overflow condition that previously enabled arbitrary code execution.