CVE-2015-6781 in Chrome
Summary
by MITRE
Integer overflow in the FontData::Bound function in data/font_data.cc in Google sfntly, as used in Google Chrome before 47.0.2526.73, allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted offset or length value within font data in an SFNT container.
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Analysis
by VulDB Data Team • 06/28/2022
The vulnerability CVE-2015-6781 represents a critical integer overflow flaw within the sfntly library's FontData::Bound function, specifically located in data/font_data.cc. This issue affects Google Chrome versions prior to 47.0.2526.73 and demonstrates how font processing mechanisms can be exploited to compromise system stability. The vulnerability stems from inadequate input validation when handling offset and length parameters within SFNT container font files, creating a scenario where maliciously crafted font data can trigger arithmetic overflow conditions that lead to unpredictable system behavior.
The technical exploitation of this vulnerability occurs when the FontData::Bound function processes font data containing crafted offset or length values that exceed the maximum representable integer values for the target platform. When these overflow conditions occur during font parsing operations, they can result in memory corruption or buffer overflows that may manifest as application crashes or potentially enable more sophisticated attack vectors. The integer overflow specifically affects the boundary checking mechanism that should validate font data ranges, allowing attackers to bypass normal validation checks and manipulate memory layout during font rendering operations.
From an operational impact perspective, this vulnerability creates significant risks for Chrome users and organizations relying on the browser for web content delivery. The remote exploitation capability means attackers can craft malicious font files that, when rendered by Chrome, trigger the overflow condition without user interaction. This makes the vulnerability particularly dangerous in web browsing scenarios where users may encounter maliciously crafted fonts in web pages, email attachments, or other digital content. The potential for unspecified other impacts suggests that beyond simple denial of service, attackers might be able to execute arbitrary code or escalate privileges depending on the execution environment.
The vulnerability aligns with CWE-190, which describes integer overflow and underflow conditions, and demonstrates how improper handling of numeric values in parsing functions can create security risks. From an ATT&CK framework perspective, this vulnerability maps to T1203, which covers Exploitation for Client Execution, and T1059, covering Command and Scripting Interpreter, as the overflow could potentially lead to code execution within the browser context. Organizations should prioritize patching affected Chrome versions and implementing additional security controls such as font filtering mechanisms, sandboxing configurations, and network-based protections to mitigate the risk of exploitation. The remediation process requires updating to Chrome version 47.0.2526.73 or later, which includes fixes that properly validate integer values and prevent overflow conditions during font data processing operations.