CVE-2016-1974 in Firefox
Summary
by MITRE
The nsScannerString::AppendUnicodeTo function in Mozilla Firefox before 45.0 and Firefox ESR 38.x before 38.7 does not verify that memory allocation succeeds, which allows remote attackers to execute arbitrary code or cause a denial of service (out-of-bounds read) via crafted Unicode data in an HTML, XML, or SVG document.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-1974 represents a critical memory safety issue within Mozilla Firefox's string handling mechanisms. This flaw exists in the nsScannerString::AppendUnicodeTo function which is part of Firefox's core rendering engine responsible for processing Unicode text data. The vulnerability affects versions prior to Firefox 45.0 and Firefox ESR 38.x versions prior to 38.7, making it a significant concern for organizations relying on these older browser versions. The issue stems from inadequate error handling during memory allocation operations, creating a pathway for malicious actors to exploit the system through carefully crafted Unicode sequences.
The technical implementation of this vulnerability involves a classic out-of-bounds memory access pattern that occurs when the function fails to validate memory allocation results before proceeding with data operations. When Firefox encounters crafted Unicode data within HTML, XML, or SVG documents, the nsScannerString::AppendUnicodeTo function attempts to allocate memory for the Unicode string processing without proper verification of allocation success. This failure creates a condition where subsequent operations may attempt to access memory locations that have not been properly allocated, leading to unpredictable behavior. The flaw specifically manifests as an out-of-bounds read condition that can be leveraged by attackers to either execute arbitrary code or cause a denial of service by triggering memory corruption.
From an operational perspective, this vulnerability presents a severe risk to enterprise environments where legacy Firefox versions may still be in use. The attack vector requires remote code execution through web-based content, making it particularly dangerous for organizations with users who browse untrusted websites or receive malicious emails containing crafted documents. The vulnerability can be exploited across multiple document formats including HTML, XML, and SVG, expanding the potential attack surface significantly. Security teams must consider that this flaw could be used in advanced persistent threat campaigns where attackers seek to establish persistent access to target systems through browser-based exploitation.
The impact of this vulnerability aligns with CWE-754 weakness classification, which deals with weakness in which an application does not properly validate or check the results of memory allocation operations. This weakness creates opportunities for attackers to manipulate memory behavior through crafted inputs that exploit the lack of proper error handling. The ATT&CK framework categorizes this vulnerability under the T1059.007 technique related to command and scripting interpreter, as the successful exploitation could lead to arbitrary code execution. Organizations should also consider this vulnerability in the context of T1211 technique for exploitation for defense evasion, as the memory corruption could be used to bypass security controls. The vulnerability's potential for denial of service makes it particularly concerning for web applications and services that depend on stable browser rendering capabilities.
Mitigation strategies for CVE-2016-1974 should prioritize immediate patching of affected Firefox versions to the latest available releases. Organizations should implement comprehensive browser update policies that ensure all systems are running supported versions with the latest security patches. Network-based mitigations including web application firewalls and content filtering solutions can provide additional protection layers while maintaining system availability. Security monitoring should include detection of unusual memory access patterns or out-of-bounds read behaviors that might indicate exploitation attempts. Regular security assessments should verify that no legacy Firefox installations remain in the environment, as these systems represent ongoing security risks. The vulnerability also underscores the importance of proper memory allocation error handling in software development practices, particularly in applications handling untrusted input data. Organizations should conduct regular security training for developers to emphasize the critical nature of proper resource management and error validation in preventing similar vulnerabilities.