CVE-2016-1968 in Firefox
Summary
by MITRE
Integer underflow in Brotli, as used in Mozilla Firefox before 45.0, allows remote attackers to execute arbitrary code or cause a denial of service (buffer overflow) via crafted data with brotli compression.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-1968 represents a critical integer underflow flaw within the Brotli compression library implementation in Mozilla Firefox versions prior to 45.0. This issue arises from insufficient input validation during the decompression process where the software fails to properly handle edge cases in the brotli compression algorithm. The flaw specifically manifests when processing crafted compressed data that triggers an integer underflow condition, which subsequently leads to improper memory allocation calculations and buffer handling. Such vulnerabilities fall under the CWE-190 category of Integer Overflow or Wraparound, where the mathematical operation results in a value that cannot be represented within the target data type, creating exploitable conditions for attackers.
The technical exploitation of this vulnerability occurs through the manipulation of compressed data streams that contain maliciously crafted parameters within the brotli compression format. When Firefox attempts to decompress such data, the integer underflow causes the system to allocate insufficient memory buffers or calculate incorrect buffer boundaries, leading to memory corruption. This memory corruption can be leveraged by remote attackers to execute arbitrary code on the victim's system or to cause a denial of service condition that crashes the browser application. The attack vector is particularly dangerous because it can be triggered through standard web browsing activities, requiring no special privileges or user interaction beyond visiting a malicious website.
The operational impact of CVE-2016-1968 extends beyond simple denial of service scenarios to encompass full remote code execution capabilities that can compromise user systems. Attackers can craft malicious web content that when loaded in Firefox, triggers the integer underflow condition and subsequently executes malicious code with the privileges of the browser process. This vulnerability affects all Firefox users running versions before 45.0, making it a widespread concern for organizations and individual users alike. The attack surface is broad as it can be delivered through various web-based vectors including malicious websites, compromised web applications, or even through email attachments that trigger browser-based decompression. The vulnerability demonstrates the critical importance of proper input validation and memory management in compression libraries, as these components are frequently targeted due to their complex nature and widespread usage.
Mitigation strategies for this vulnerability primarily involve upgrading to Mozilla Firefox version 45.0 or later where the integer underflow has been addressed through proper input validation and boundary checking mechanisms. Organizations should implement comprehensive patch management procedures to ensure all Firefox installations are updated promptly. Additionally, network administrators can deploy web application firewalls or content filtering solutions that can detect and block suspicious brotli compressed content. The fix implemented by Mozilla typically involves adding additional checks to validate the integer calculations during decompression and ensuring that buffer allocations are properly bounded. Security teams should also monitor for any potential exploitation attempts through network traffic analysis and implement proper logging of browser decompression activities to detect anomalous behavior patterns. This vulnerability highlights the importance of adhering to secure coding practices as outlined in the OWASP Secure Coding Practices and the ATT&CK framework's defense evasion techniques, particularly those related to memory corruption and code execution primitives.