CVE-2008-1806 in FreeType
Summary
by MITRE
Integer overflow in FreeType2 before 2.3.6 allows context-dependent attackers to execute arbitrary code via a crafted set of 16-bit length values within the Private dictionary table in a Printer Font Binary (PFB) file, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 08/12/2019
The vulnerability described in CVE-2008-1806 represents a critical integer overflow flaw within the FreeType2 font rendering library that was prevalent in versions prior to 2.3.6. This vulnerability resides in the handling of Printer Font Binary file formats, which are commonly used for distributing printer fonts and are processed by various applications including web browsers, document viewers, and desktop publishing software. The flaw specifically manifests when the library encounters a crafted set of 16-bit length values within the Private dictionary table of a PFB file, creating a condition where arithmetic operations result in integer overflow.
The technical implementation of this vulnerability exploits the way FreeType2 processes font data structures, particularly focusing on how it calculates buffer sizes for heap allocations. When the library encounters malformed 16-bit length values within the Private dictionary table, it performs arithmetic operations that exceed the maximum representable value for a 32-bit integer, causing an integer overflow condition. This overflow subsequently leads to an incorrect calculation of buffer size needed for heap allocation, resulting in a heap-based buffer overflow. The attacker-controlled data flows directly into the memory allocation process, where the overflowed value becomes the basis for determining how much memory to allocate for processing the font data.
The operational impact of this vulnerability extends across multiple attack vectors since FreeType2 is widely integrated into numerous software applications and operating systems. Any application that processes PFB font files, including web browsers, PDF viewers, office suites, and image processing software, becomes potentially vulnerable to exploitation. The context-dependent nature of this attack means that exploitation requires a specific combination of conditions, including the presence of a malicious PFB file and the target application's processing of that file through the vulnerable FreeType2 library. Attackers can leverage this vulnerability to execute arbitrary code with the privileges of the affected application, potentially leading to complete system compromise.
This vulnerability aligns with CWE-190, which describes integer overflow conditions, and specifically maps to the category of heap-based buffer overflows that occur due to improper integer handling during memory allocation. From an ATT&CK framework perspective, this vulnerability corresponds to techniques involving code injection through malicious file formats, specifically T1203 - Exploitation for Client Execution and T1068 - Exploitation for Privilege Escalation. The attack surface is particularly concerning given that PFB files are commonly encountered in legitimate document processing workflows, making social engineering attacks that deliver malicious fonts particularly effective. Organizations should prioritize patching affected systems to address this vulnerability, as it represents a significant risk to system security and can be exploited remotely through web-based content or through local file processing.
Mitigation strategies should include immediate deployment of FreeType2 version 2.3.6 or later, which contains the necessary fixes to properly handle integer overflow conditions in PFB file processing. Additionally, organizations should implement content filtering mechanisms to restrict processing of untrusted font files and consider sandboxing applications that handle font rendering to limit potential damage from successful exploitation attempts. Regular security assessments should verify that all applications using FreeType2 have been updated and that no legacy versions remain in use.