CVE-2016-1526 in Graphite
Summary
by MITRE
The TtfUtil:LocaLookup function in TtfUtil.cpp in Libgraphite in Graphite 2 1.2.4, as used in Mozilla Firefox before 43.0 and Firefox ESR 38.x before 38.6.1, incorrectly validates a size value, which allows remote attackers to obtain sensitive information or cause a denial of service (out-of-bounds read and application crash) via a crafted Graphite smart font.
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Analysis
by VulDB Data Team • 10/23/2024
The vulnerability identified as CVE-2016-1526 represents a critical security flaw within the Graphite 2 library's TtfUtil component, specifically in the LocaLookup function located in TtfUtil.cpp. This issue affects Mozilla Firefox versions prior to 43.0 and Firefox ESR 38.x versions before 38.6.1, creating a significant attack surface for remote threat actors. The flaw resides in the improper validation of size parameters within the font processing pipeline, which forms a fundamental component of the browser's typography rendering system. When a maliciously crafted Graphite smart font is processed, the vulnerable code fails to properly validate the size value, leading to exploitable memory access patterns that can be leveraged for various attack vectors.
The technical implementation of this vulnerability stems from insufficient input validation mechanisms within the LocaLookup function, which is responsible for locating and processing font data structures. This function processes the location table of TrueType fonts, where it expects specific size parameters to define the boundaries of data segments. However, the validation logic fails to properly check whether the size value falls within acceptable ranges, allowing attackers to craft font files with malformed size parameters. The vulnerability manifests as an out-of-bounds read condition that occurs when the function attempts to access memory locations beyond the allocated buffer boundaries. This memory access violation can result in information disclosure through data leakage from adjacent memory segments or cause application crashes through forced termination of the rendering process.
The operational impact of CVE-2016-1526 extends beyond simple denial of service conditions, as it creates opportunities for information disclosure attacks that could potentially expose sensitive data from the browser's memory space. Attackers can exploit this vulnerability by embedding malicious Graphite smart fonts within web pages, documents, or other media that trigger font processing within the affected Firefox versions. The out-of-bounds read behavior can inadvertently expose memory contents including cryptographic keys, session tokens, or other sensitive information stored in adjacent memory locations. This vulnerability directly maps to CWE-129, which addresses improper validation of the length of input data, and can be categorized under ATT&CK technique T1059.007 for execution through scripting languages, as the attack vector leverages web-based scripting to trigger the vulnerable font processing code.
Mitigation strategies for this vulnerability require immediate patching of affected Firefox installations to version 43.0 or later for regular releases and 38.6.1 for ESR versions, as these releases contain the necessary code modifications to properly validate size parameters in the LocaLookup function. Additionally, system administrators should consider implementing content security policies that restrict the loading of untrusted font resources and employ web application firewalls that can detect and block malicious font files. The fix implemented in the patched versions involves strengthening the input validation logic to ensure that size values are properly bounded and validated before any memory access operations occur. Organizations should also conduct comprehensive vulnerability assessments to identify any other applications that might be using the vulnerable Graphite 2 library, as the same flaw could exist in other software components that rely on the same font processing functionality. Network monitoring should be enhanced to detect potential exploitation attempts through unusual font processing patterns or memory access violations that may indicate active exploitation of this vulnerability.