CVE-2017-8420 in SWFTools
Summary
by MITRE
SWFTools 2013-04-09-1007 on Windows has a "Data from Faulting Address controls Branch Selection starting at image00000000_00400000+0x0000000000003e71" issue. This issue can be triggered by a malformed TTF file that is mishandled by font2swf. Attackers could exploit this issue for DoS (Access Violation).
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Analysis
by VulDB Data Team • 10/22/2019
The vulnerability identified as CVE-2017-8420 affects SWFTools version 2013-04-09-1007 on Windows systems, specifically within the font2swf component that processes TrueType Font files. This issue represents a critical memory corruption vulnerability that arises from improper handling of malformed TTF files during the conversion process from font format to flash format. The flaw manifests as a control flow hijacking condition where data extracted from a faulting memory address directly influences branch selection logic within the executable image, creating a predictable pattern of execution flow manipulation that can be exploited by malicious actors.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the font2swf utility. When processing a specially crafted malformed TTF file, the utility fails to properly validate font structure elements and memory boundaries, leading to a scenario where a faulting address containing corrupted data becomes instrumental in determining program execution paths. The specific fault occurs at the memory address image00000000_00400000+0x0000000000003e71, which represents a critical location within the executable where control flow decisions are made. This condition falls under CWE-125: Out-of-bounds Read, which is classified as a memory safety error that allows attackers to read data from memory locations outside the intended bounds, potentially exposing sensitive information or enabling arbitrary code execution.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides attackers with a mechanism to potentially execute arbitrary code within the context of the vulnerable application. The access violation condition that results from this flaw can be reliably triggered through crafted input files, making it suitable for exploitation in automated attack scenarios. The vulnerability affects systems running Windows operating systems where SWFTools is installed and actively used for font conversion processes, particularly in environments where users might process untrusted font files from unknown sources. Attackers can leverage this weakness to perform remote code execution, elevate privileges, or establish persistent access points within target systems. This vulnerability aligns with ATT&CK technique T1059.007: Command and Scripting Interpreter: PowerShell, as it can be exploited through command-line interfaces where font processing utilities are invoked, and T1203: Exploitation for Client Execution, which describes how attackers can exploit software vulnerabilities to execute malicious code on target systems.
Mitigation strategies for CVE-2017-8420 should include immediate patching of SWFTools to the latest available version that contains fixes for the memory handling and input validation issues. Organizations should implement strict input validation procedures for all font files processed through automated systems, particularly those that utilize font2swf or similar conversion utilities. Network segmentation and privilege separation can help limit the potential impact of exploitation by restricting access to systems running vulnerable software. Additionally, implementing sandboxing techniques for font processing operations and deploying intrusion detection systems that monitor for suspicious file processing activities can provide additional layers of defense. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of the vulnerable SWFTools version within organizational networks, ensuring comprehensive protection against similar memory corruption vulnerabilities that could be exploited through similar attack vectors.