CVE-2017-6847 in PoDoFo
Summary
by MITRE
The PoDoFo::PdfVariant::DelayedLoad function in PdfVariant.h in PoDoFo 0.9.4 allows remote attackers to cause a denial of service (NULL pointer dereference) via a crafted file.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2017-6847 resides within the PoDoFo library version 0.9.4, specifically in the PdfVariant.h header file where the PoDoFo::PdfVariant::DelayedLoad function operates. This flaw represents a classic null pointer dereference issue that can be exploited by remote attackers through the careful crafting of malicious PDF files. The vulnerability falls under the category of denial of service attacks where the target system crashes or becomes unresponsive due to improper handling of null references during PDF parsing operations. The PoDoFo library serves as a widely used C++ library for reading and writing PDF documents, making this vulnerability particularly concerning for applications that process untrusted PDF content.
The technical implementation of this vulnerability occurs when the DelayedLoad function attempts to access a null pointer reference during the parsing of PDF variants within malformed documents. When a crafted PDF file contains specific malformed data structures, the function fails to properly validate pointer states before dereferencing them, leading to a segmentation fault or access violation. This behavior aligns with CWE-476 which specifically addresses null pointer dereference conditions in software implementations. The vulnerability demonstrates a lack of proper input validation and error handling within the PDF parsing pipeline, where the library does not adequately sanitize or validate the structure of PDF objects before attempting to process them.
The operational impact of CVE-2017-6847 extends beyond simple service disruption as it can be leveraged in various attack scenarios including web application exploitation, email attachment processing, and document management systems. Applications utilizing PoDoFo for PDF handling become vulnerable to remote code execution risks if attackers can manipulate the parsing flow through crafted inputs. This vulnerability is particularly dangerous in environments where PDF processing is automated or occurs without user intervention, such as web servers, document conversion services, or enterprise content management systems. The attack vector requires minimal privileges and can be executed through standard PDF file delivery mechanisms, making it an attractive target for automated exploitation campaigns. The vulnerability also maps to ATT&CK technique T1203 which covers legitimate programs used for exploitation, particularly when PDF processing is involved in routine system operations.
Mitigation strategies for CVE-2017-6847 primarily involve upgrading to PoDoFo version 0.9.5 or later where the vulnerability has been patched through proper null pointer validation and input sanitization. Organizations should implement comprehensive input validation measures that include checking pointer states before dereferencing operations, implementing proper error handling mechanisms, and conducting regular security assessments of PDF processing components. Additionally, deploying network segmentation, application whitelisting, and sandboxing techniques can provide additional defense layers against exploitation attempts. Security monitoring should include detection of unusual PDF processing patterns and memory access violations that may indicate exploitation attempts. The fix implemented in subsequent versions demonstrates proper defensive programming practices that align with industry standards for secure coding and memory management, addressing the root cause through enhanced validation rather than merely patching the symptom.