CVE-2017-8787 in PoDoFo
Summary
by MITRE
The PoDoFo::PdfXRefStreamParserObject::ReadXRefStreamEntry function in base/PdfXRefStreamParserObject.cpp:224 in PoDoFo 0.9.5 allows remote attackers to cause a denial of service (heap-based buffer over-read) or possibly have unspecified other impact via a crafted PDF file.
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Analysis
by VulDB Data Team • 09/24/2020
The vulnerability identified as CVE-2017-8787 resides within the PoDoFo library version 0.9.5, specifically within the PdfXRefStreamParserObject component responsible for parsing cross-reference streams in pdf documents. This flaw manifests in the ReadXRefStreamEntry function located at base/PdfXRefStreamParserObject.cpp line 224, where improper input validation leads to a heap-based buffer over-read condition. The vulnerability represents a critical security flaw that can be exploited remotely through maliciously crafted pdf files, potentially leading to system instability and denial of service conditions. The issue stems from inadequate bounds checking during the parsing of cross-reference stream entries, which are essential components of pdf file structure that maintain references to object locations within the document. When an attacker provides a specially crafted pdf file containing malformed cross-reference stream data, the parser fails to properly validate the input boundaries, allowing memory access beyond allocated buffer limits.
The technical impact of this vulnerability aligns with CWE-129, which describes improper validation of array indices, and CWE-787, which covers out-of-bounds write operations. The heap-based buffer over-read occurs when the parser attempts to read memory locations beyond the allocated buffer space, potentially exposing sensitive data or causing application crashes. The operational implications extend beyond simple denial of service as this vulnerability could potentially enable more sophisticated attacks depending on the execution environment and memory layout. Attackers can leverage this flaw to cause unpredictable behavior in pdf processing applications, including application termination, memory corruption, or in some cases, arbitrary code execution if the memory corruption affects critical program structures. The vulnerability affects any application that utilizes PoDoFo library version 0.9.5 for pdf document processing, including document management systems, pdf viewers, and content management platforms.
From an attack perspective, this vulnerability maps to several ATT&CK techniques including T1203, which involves legitimate user privileges to execute malicious code through application loading, and T1059, which covers command and scripting interpreter usage. The exploitation process requires an attacker to craft a malicious pdf file that triggers the vulnerable parsing code path when the target application attempts to read the cross-reference stream. The vulnerability is particularly concerning because pdf files are commonly used in enterprise environments and are frequently processed automatically by various applications, making the attack surface broad and potentially automated. Security professionals should consider this vulnerability when assessing pdf processing applications and implementing security controls for document handling systems. The impact assessment should include evaluating all applications that rely on PoDoFo library for pdf processing, as the vulnerability could be leveraged in phishing campaigns, document-based attacks, or supply chain compromises where malicious pdf files are distributed to unsuspecting users.
Mitigation strategies should prioritize immediate patching of affected PoDoFo library versions to 0.9.6 or later, which contains the necessary fixes for the buffer over-read condition. Organizations should also implement pdf file scanning and validation procedures as part of their security controls, including sandboxing pdf processing operations to contain potential exploitation attempts. Network-based protections such as pdf content filtering and deep packet inspection can help identify and block malicious pdf files before they reach end-user applications. Additionally, application developers should implement proper input validation and bounds checking in their pdf processing code, regardless of the underlying library used, to prevent similar issues from occurring in custom implementations. The vulnerability highlights the importance of regular security updates and the need for comprehensive security testing of document processing libraries, particularly those handling binary formats with complex parsing requirements.