CVE-2017-18185 in QPDF
Summary
by MITRE
An issue was discovered in QPDF before 7.0.0. There is a large heap-based out-of-bounds read in the Pl_Buffer::write function in Pl_Buffer.cc. It is caused by an integer overflow in the PNG filter.
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Analysis
by VulDB Data Team • 02/06/2023
The vulnerability identified as CVE-2017-18185 represents a critical heap-based out-of-bounds read flaw in the QPDF library version 7.0.0 and earlier. This issue manifests within the Pl_Buffer::write function located in the Pl_Buffer.cc source file, where the vulnerability is specifically triggered by an integer overflow occurring during PNG filter processing. The flaw demonstrates significant security implications as it allows for memory access beyond the allocated buffer boundaries, potentially enabling attackers to read sensitive data from adjacent memory locations or cause application instability through memory corruption.
The technical root cause of this vulnerability lies in the improper handling of integer values during PNG filter operations within the QPDF library's buffer management system. When processing PNG files, the library performs calculations that involve integer overflow conditions, leading to incorrect buffer size calculations and subsequent out-of-bounds memory reads. This type of vulnerability falls under the CWE-129 weakness category, which specifically addresses issues related to insufficient bounds checking of array data, and more broadly aligns with CWE-190, which encompasses integer overflow and wraparound conditions. The integer overflow occurs during the computation of buffer sizes needed for PNG filter processing, where the calculation results in a value that exceeds the maximum representable integer, causing the subsequent memory operations to access invalid memory regions.
From an operational standpoint, this vulnerability poses substantial risks to systems that process untrusted PNG files through the QPDF library. Attackers could exploit this flaw by crafting malicious PNG files that trigger the integer overflow condition, potentially leading to information disclosure, application crashes, or in more severe cases, arbitrary code execution depending on the specific memory layout and exploitation techniques employed. The impact extends beyond simple denial-of-service scenarios as the out-of-bounds read could expose sensitive information from adjacent memory segments, including cryptographic keys, user credentials, or other confidential data that may be stored in memory near the affected buffer regions. This vulnerability is particularly concerning in environments where QPDF is used for processing documents from untrusted sources such as web applications, document management systems, or any service handling user-uploaded content.
The exploitation of this vulnerability requires careful crafting of PNG files that will trigger the specific integer overflow condition during the Pl_Buffer::write operation. Security practitioners should note that this flaw represents a classic example of how seemingly benign file processing operations can expose critical security vulnerabilities through improper input validation and buffer management. Mitigation strategies should focus on immediate patching of the QPDF library to version 7.0.0 or later, where the integer overflow has been addressed through proper bounds checking and overflow protection mechanisms. Additionally, implementing proper input validation and sanitization measures for PNG files, along with runtime monitoring for abnormal memory access patterns, can provide additional layers of defense. Organizations should also consider implementing sandboxing techniques when processing untrusted document formats and regularly review their document processing pipelines for similar vulnerabilities that might exist in other third-party libraries or components. The ATT&CK framework categorizes this vulnerability under the T1059.007 technique for execution through scripting languages and T1203 for exploitation of software vulnerabilities, highlighting the need for comprehensive security measures that address both the immediate patching requirements and broader defensive strategies against similar classes of vulnerabilities.