CVE-2017-5855 in PoDoFo
Summary
by MITRE
The PoDoFo::PdfParser::ReadXRefSubsection function in PdfParser.cpp 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 • 09/03/2020
The vulnerability identified as CVE-2017-5855 represents a critical denial of service weakness within the PoDoFo PDF processing library version 0.9.4. This flaw exists in the PdfParser.cpp file within the PoDoFo::PdfParser::ReadXrefSubsection function, which is responsible for parsing cross-reference sections in PDF documents. The vulnerability arises when the library encounters a specially crafted PDF file that contains malformed cross-reference data, leading to a NULL pointer dereference condition during the parsing process. This type of vulnerability falls under the category of improper input validation and can be classified as CWE-476, which specifically addresses NULL pointer dereference issues in software implementations.
The technical execution of this vulnerability occurs when an attacker constructs a PDF file containing malformed cross-reference subsections that cause the PdfParser::ReadXrefSubsection function to attempt to dereference a NULL pointer. When the parser processes such a crafted file, it fails to properly validate the structure of the cross-reference table entries before attempting to access them, resulting in the application crashing or becoming unresponsive. This behavior constitutes a denial of service attack since legitimate users cannot process the affected PDF files, and the application becomes unavailable for normal operations. The vulnerability is particularly concerning because PDF processing libraries are widely used across numerous applications and systems, making this a potential vector for widespread service disruption.
The operational impact of CVE-2017-5855 extends beyond simple service interruption, as it represents a fundamental flaw in how the PoDoFo library handles malformed input data. When exploited, this vulnerability can affect any application that relies on PoDoFo for PDF processing, including document management systems, web applications, email clients, and content management platforms. The attack requires only the ability to deliver a malicious PDF file to the target system, making it particularly dangerous in environments where users might encounter untrusted PDF content. From an attack framework perspective, this vulnerability aligns with techniques described in the MITRE ATT&CK framework under the T1059 category of 'Command and Scripting Interpreter' and T1499 'Endpoint Denial of Service', as it enables an attacker to disrupt services through malformed input processing.
Organizations using PoDoFo version 0.9.4 should implement immediate mitigations to address this vulnerability. The most effective approach involves upgrading to a patched version of the PoDoFo library where the cross-reference parsing logic has been strengthened to properly validate input data before attempting to dereference pointers. Additionally, implementing input validation measures at the application level can provide defense in depth, including sanitizing PDF files before processing and implementing timeout mechanisms for PDF parsing operations. System administrators should also consider deploying intrusion detection systems that can identify suspicious PDF file patterns and network-based protections that prevent the delivery of potentially malicious PDF content. The vulnerability demonstrates the critical importance of proper error handling and input validation in security-critical libraries, as highlighted in industry best practices for secure coding standards and the OWASP Top Ten security risks.