CVE-2015-6758 in Chrome
Summary
by MITRE
The CPDF_Document::GetPage function in fpdfapi/fpdf_parser/fpdf_parser_document.cpp in PDFium, as used in Google Chrome before 46.0.2490.71, does not properly perform a cast of a dictionary object, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted PDF document.
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Analysis
by VulDB Data Team • 06/21/2022
The vulnerability identified as CVE-2015-6758 resides within the PDFium library's CPDF_Document::GetPage function, specifically in the fpdfapi/fpdf_parser/fpdf_parser_document.cpp file. This flaw manifests in Google Chrome versions prior to 46.0.2490.71, representing a critical security issue that affects the browser's PDF rendering capabilities. The vulnerability stems from improper casting of dictionary objects during PDF document parsing, creating a potential attack vector that remote adversaries can exploit through maliciously crafted PDF files. This issue falls under the category of improper type handling within the PDF processing pipeline, where the system fails to validate or properly convert dictionary objects to their expected types before processing.
The technical implementation of this vulnerability involves a specific type casting error within the PDF document parsing logic that processes page objects. When PDFium encounters a dictionary object that should represent a page structure, the GetPage function fails to properly cast this object to the expected page dictionary type. This improper casting can lead to memory corruption or invalid memory access patterns, as the system attempts to interpret the improperly cast object as a valid page structure. The flaw essentially allows attackers to manipulate the type information during parsing, causing the application to follow incorrect execution paths that result in system instability. This type of vulnerability is categorized as a weakness in the program's data handling and type validation mechanisms, aligning with CWE-121 which addresses buffer overflow conditions and CWE-129 which covers improper validation of array indices.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable more sophisticated attacks. Remote attackers can craft PDF documents that trigger the flawed casting behavior, leading to system crashes, browser instability, or in some cases, arbitrary code execution depending on the memory corruption patterns. The vulnerability's potential for unspecified other impacts suggests that attackers might be able to leverage this flaw as a stepping stone for more advanced exploitation techniques, potentially leading to privilege escalation or information disclosure. Given that Chrome's PDF viewer is widely used and the vulnerability affects a core parsing function, the attack surface is substantial, making this flaw particularly dangerous in targeted attack scenarios where adversaries might combine this vulnerability with other exploits.
Mitigation strategies for CVE-2015-6758 primarily focus on immediate browser updates to versions that contain the patched PDFium library. Organizations should ensure all Chrome installations are updated to version 46.0.2490.71 or later, as this release includes the necessary fixes for the improper casting issue. Additionally, implementing network-level controls such as PDF file scanning and sandboxing mechanisms can provide additional defense-in-depth layers. Security teams should also consider disabling PDF rendering in browsers where it is not essential, particularly in high-security environments. The fix implemented by Google involved proper validation and casting of dictionary objects before processing, ensuring that the system maintains type safety throughout the PDF parsing process. This vulnerability demonstrates the importance of robust input validation and type safety in PDF processing libraries, aligning with ATT&CK technique T1203 which covers exploitation for privilege escalation and T1059 which addresses command and scripting interpreters. Organizations should also implement regular security assessments of their browser environments and maintain updated threat intelligence to identify similar vulnerabilities that might affect other PDF rendering components in their infrastructure.