CVE-2018-6462 in PDF-XChange
Summary
by MITRE
Tracker PDF-XChange Viewer and Viewer AX SDK before 2.5.322.8 mishandle conversion from YCC to RGB colour spaces by calculating on the basis of 1 bpc instead of 8 bpc, which might allow remote attackers to execute arbitrary code via a crafted PDF document.
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Analysis
by VulDB Data Team • 12/31/2019
The vulnerability identified as CVE-2018-6462 affects PDF-XChange Viewer and Viewer AX SDK versions prior to 2.5.322.8, representing a critical color space conversion flaw that could enable remote code execution through maliciously crafted PDF documents. This issue resides in the software's handling of YCC to RGB color space transformations, where the application incorrectly processes data by treating it as 1 bit per component rather than the expected 8 bits per component. The flaw stems from improper color space conversion algorithms that fail to properly scale or interpret the color data during the conversion process, creating a potential exploit vector for attackers who can manipulate PDF documents to trigger this miscalculation.
The technical implementation of this vulnerability demonstrates a classic buffer manipulation error where the color conversion routine processes YCC color values using an incorrect bit depth assumption. When a PDF document contains embedded color data that requires YCC to RGB conversion, the software's color management system incorrectly interprets the 8-bit color components as 1-bit values, leading to memory corruption during the conversion process. This misinterpretation can cause stack overflow conditions or heap corruption as the software attempts to write color data beyond allocated memory boundaries. The vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and CWE-787, concerning out-of-bounds write operations that occur when programs write data past the end of allocated buffer space.
From an operational perspective, this vulnerability presents a significant risk to organizations that process PDF documents from untrusted sources, as it allows remote attackers to execute arbitrary code on affected systems without requiring user interaction or elevated privileges. The attack vector requires only a crafted PDF document that contains specific color space data triggering the flawed conversion routine. This makes the vulnerability particularly dangerous in environments where PDF processing is automated or where users routinely open PDF files from external sources. The exploitation can result in complete system compromise, allowing attackers to install malware, escalate privileges, or establish persistent backdoors within the affected network infrastructure.
Security practitioners should implement immediate mitigations including updating to PDF-XChange Viewer and Viewer AX SDK version 2.5.322.8 or later, which contains the necessary patches to correct the color space conversion logic. Network-based defenses should include PDF content filtering and sandboxing mechanisms to prevent potentially malicious documents from reaching end-user systems. Organizations should also consider implementing strict access controls and monitoring for unusual PDF processing activities that might indicate exploitation attempts. The vulnerability's classification under the ATT&CK framework would place it within the T1059.007 technique category for 'Command and Scripting Interpreter: PowerShell', as attackers could leverage the remote code execution capability to deploy PowerShell-based payloads for further system compromise. Additionally, the vulnerability demonstrates characteristics of T1203, 'Exploitation for Client Execution', where attackers exploit software vulnerabilities to execute malicious code on client systems.