CVE-2018-20751 in PoDoFo
Summary
by MITRE
An issue was discovered in crop_page in PoDoFo 0.9.6. For a crafted PDF document, pPage->GetObject()->GetDictionary().AddKey(PdfName("MediaBox"),var) can be problematic due to the function GetObject() being called for the pPage NULL pointer object. The value of pPage at this point is 0x0, which causes a NULL pointer dereference.
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Analysis
by VulDB Data Team • 07/04/2023
The vulnerability identified as CVE-2018-20751 represents a critical null pointer dereference flaw within the PoDoFo PDF processing library version 0.9.6. This issue manifests in the crop_page functionality where the library fails to properly validate pointer references before attempting to access object members. The flaw occurs when processing specially crafted PDF documents that trigger the execution path where pPage->GetObject()->GetDictionary().AddKey(PdfName("MediaBox"),var) is invoked. The root cause stems from the pPage variable holding a null pointer value of 0x0 at the moment of function execution, creating an immediate dereference of a null pointer that results in application crash or potential memory corruption.
This vulnerability falls under the category of CWE-476_NULL_Pointer_Dereference, which is classified as a common weakness in software development practices where programs attempt to access memory through a pointer that has not been properly initialized or validated. The operational impact of this flaw extends beyond simple application crashes, as it represents a potential denial of service condition that could be exploited by malicious actors to disrupt PDF processing workflows. The vulnerability demonstrates poor error handling and input validation practices within the PDF parsing engine, where the library does not adequately check for null pointer conditions before attempting to invoke methods on potentially uninitialized objects. Attackers could leverage this weakness by crafting malicious PDF files that specifically trigger this code path during normal PDF processing operations.
The security implications of CVE-2018-20751 align with ATT&CK technique T1203_Access_Control_Bypass, as this vulnerability could potentially enable attackers to cause system instability or denial of service conditions in applications that rely on PoDoFo for PDF manipulation. The flaw affects any system or application that utilizes PoDoFo 0.9.6 for PDF processing, including document management systems, PDF viewers, and content management platforms. The vulnerability is particularly concerning because it can be triggered through normal PDF document processing without requiring any special privileges or user interaction beyond opening a maliciously crafted file. The null pointer dereference creates an opportunity for attackers to cause application termination or potentially execute arbitrary code if the memory corruption leads to further exploitable conditions.
Mitigation strategies for this vulnerability include immediate patching of PoDoFo to version 0.9.7 or later where the null pointer validation has been implemented. Organizations should also implement input validation measures that filter or sanitize PDF documents before processing them through PoDoFo libraries. Additional defensive measures include deploying application sandboxing techniques, implementing strict file format validation, and monitoring for abnormal application behavior that might indicate exploitation attempts. The fix typically involves adding proper null pointer checks before calling GetObject() method and ensuring that all pointer validations occur before object member access. System administrators should also consider implementing network-based intrusion detection systems that can identify and block suspicious PDF file patterns that might trigger this vulnerability during processing.