CVE-2016-2838 in Firefox
Summary
by MITRE
Heap-based buffer overflow in the nsBidi::BracketData::AddOpening function in Mozilla Firefox before 48.0 and Firefox ESR 45.x before 45.3 allows remote attackers to execute arbitrary code via directional content in an SVG document.
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Analysis
by VulDB Data Team • 10/23/2024
The vulnerability identified as CVE-2016-2838 represents a critical heap-based buffer overflow affecting Mozilla Firefox versions prior to 48.0 and Firefox ESR 45.x versions prior to 45.3. This flaw resides within the nsBidi::BracketData::AddOpening function, which is responsible for handling bidirectional text processing in the browser's rendering engine. The vulnerability specifically manifests when processing directional content within SVG documents, creating a potential remote code execution vector that could be exploited by attackers.
The technical nature of this vulnerability stems from improper bounds checking within the bracket data handling mechanism of Firefox's Unicode bidirectional algorithm implementation. When the browser encounters SVG content containing directional formatting elements, the nsBidi::BracketData::AddOpening function fails to properly validate the size of data being written to heap-allocated memory structures. This inadequate input validation allows an attacker to craft malicious SVG documents that, when rendered by the vulnerable browser, trigger a buffer overflow condition in the heap memory space. The flaw is classified under CWE-121 as a heap-based buffer overflow, which occurs when more data is written to a buffer than it can hold, potentially overwriting adjacent memory locations.
The operational impact of CVE-2016-2838 extends beyond simple code execution, as it represents a sophisticated attack vector that could be leveraged for privilege escalation and system compromise. Attackers could craft specially designed SVG documents containing malicious directional content that, when opened in a vulnerable Firefox instance, would trigger the buffer overflow and potentially allow arbitrary code execution with the privileges of the browser process. This vulnerability particularly affects web applications and content management systems that might process user-uploaded SVG files or display third-party SVG content without proper sanitization. The attack requires no user interaction beyond visiting a malicious website or opening a crafted document, making it particularly dangerous in phishing campaigns and drive-by download scenarios.
Mitigation strategies for CVE-2016-2838 primarily focus on immediate browser updates and application-level protections. Organizations should prioritize updating to Firefox versions 48.0 or later for regular releases, and Firefox ESR 45.3 or later for extended support releases, which contain the patched implementation of the nsBidi::BracketData::AddOpening function. Additionally, administrators should implement content filtering mechanisms that sanitize SVG content before processing, particularly focusing on removing or neutralizing directional formatting attributes that could trigger the vulnerable code path. Network-level protections such as web application firewalls and security headers can help detect and prevent exploitation attempts. The vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and demonstrates the importance of proper memory management in web browser implementations. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of the vulnerable browser versions within organizational networks.