CVE-2019-9959 in Poppler
Summary
by MITRE
The JPXStream::init function in Poppler 0.78.0 and earlier doesn't check for negative values of stream length, leading to an Integer Overflow, thereby making it possible to allocate a large memory chunk on the heap, with a size controlled by an attacker, as demonstrated by pdftocairo.
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Analysis
by VulDB Data Team • 11/05/2023
The vulnerability described in CVE-2019-9959 represents a critical integer overflow flaw within the JPXStream::init function of the Poppler PDF library version 0.78.0 and earlier. This issue manifests when the library processes JPEG2000 streams within PDF documents, specifically failing to validate stream length parameters for negative values. The absence of proper input validation creates a scenario where an attacker can manipulate the stream length parameter to trigger an integer overflow condition, which subsequently results in the allocation of an unexpectedly large memory chunk on the heap. This vulnerability is particularly concerning because it allows for controlled memory allocation that can be leveraged for various malicious purposes including denial of service attacks and potentially more sophisticated exploitation techniques.
The technical implementation of this vulnerability stems from the lack of proper bounds checking within the JPXStream::init function, which is part of the broader Poppler library used for PDF rendering and processing. When the function processes a JPEG2000 stream, it accepts a length parameter that should represent the size of the data to be read. However, without validation of this parameter for negative values, an attacker can craft a malicious PDF document containing a specially formatted JPEG2000 stream with a negative length value. This negative value, when processed through the integer arithmetic operations, causes an overflow that results in a much larger unsigned integer value than intended, leading to the allocation of an enormous memory block. The vulnerability specifically affects the pdftocairo utility, which is part of the Poppler suite and is commonly used for converting PDF documents to various image formats, making it a potential vector for attacks against systems that process PDF documents.
The operational impact of CVE-2019-9959 extends beyond simple memory consumption issues, as it represents a potential pathway for denial of service attacks that can consume system resources and potentially crash applications. The vulnerability can be exploited by sending a specially crafted PDF document to any application that utilizes the vulnerable Poppler library, including web browsers, PDF viewers, and document processing systems. When such a document is processed, the integer overflow causes the application to attempt to allocate a massive amount of memory, which can lead to system instability, application crashes, or complete system resource exhaustion. This makes the vulnerability particularly dangerous in server environments where PDF processing is common, as it could be used to disrupt services or potentially as part of a larger attack chain. The vulnerability aligns with CWE-190, which describes integer overflow conditions, and represents a classic example of how improper input validation can lead to memory allocation issues. From an attacker's perspective, this vulnerability fits into the ATT&CK technique of resource exhaustion, where the attacker consumes system resources to prevent legitimate use of services.
The mitigation strategy for CVE-2019-9959 involves immediate upgrading of the Poppler library to version 0.79.0 or later, where the integer overflow has been addressed through proper input validation. System administrators should prioritize patching all affected systems that process PDF documents, particularly those running web applications, email servers, or document management systems that utilize the vulnerable library. Additionally, implementing proper input validation at the application level can provide defense-in-depth, ensuring that even if an attacker manages to bypass the library-level fix, the application itself can detect and reject malformed PDF documents. Organizations should also consider implementing sandboxing techniques for PDF processing and monitoring for unusual memory allocation patterns that might indicate exploitation attempts. The fix implemented in the patched versions involves adding proper checks for negative stream length values and ensuring that the integer overflow cannot occur during memory allocation, thereby preventing the attacker-controlled memory allocation that was previously possible.