CVE-2019-12958 in Xpdf
Summary
by MITRE
In Xpdf 4.01.01, a heap-based buffer over-read could be triggered in FoFiType1C::convertToType0 in fofi/FoFiType1C.cc when it is trying to access the second privateDicts array element, because the privateDicts array has only one element allocated.
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Analysis
by VulDB Data Team • 10/07/2023
The vulnerability identified as CVE-2019-12958 represents a critical heap-based buffer over-read flaw within the Xpdf document processing library version 4.01.01. This issue manifests in the FoFiType1C::convertToType0 function located in the fofi/FoFiType1C.cc source file, where improper memory management leads to unauthorized data access patterns that can compromise system integrity. The flaw specifically occurs during the processing of Type1C font data structures, which are commonly encountered in PDF documents and PostScript files that utilize embedded font resources.
The technical root cause stems from a fundamental mismatch between allocated memory resources and the code's assumptions about array dimensions. The privateDicts array is initialized with only a single element allocation, yet the conversion process attempts to access the second element without proper bounds checking or validation. This memory access violation creates a scenario where the application reads beyond the allocated heap memory boundaries, potentially exposing sensitive data from adjacent memory regions or causing application instability through memory corruption. Such buffer over-read conditions fall under the CWE-125 vulnerability category, which specifically addresses out-of-bounds read errors that can lead to information disclosure or system compromise.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can be exploited by malicious actors to gain unauthorized access to sensitive information stored in adjacent memory locations. When processing specially crafted PDF files containing malformed Type1C font data, the vulnerable Xpdf library can be forced to read memory that may contain other application data, configuration information, or even cryptographic keys. This makes the vulnerability particularly dangerous in environments where PDF processing is automated or where documents are processed without proper sanitization. The attack surface is broad since Xpdf is widely used across various applications and systems for PDF rendering and processing, including web browsers, document viewers, and server-side applications.
Mitigation strategies for CVE-2019-12958 should focus on immediate patching of affected Xpdf installations to version 4.01.02 or later, which contains the necessary memory bounds checking and array validation fixes. Organizations should implement comprehensive input validation for all PDF processing workflows, particularly those involving untrusted documents from external sources. Network administrators should consider deploying intrusion detection systems that can identify suspicious PDF processing patterns and implement sandboxing techniques to isolate PDF rendering operations. Additionally, security teams should conduct thorough vulnerability assessments to identify all systems running affected Xpdf versions and establish monitoring procedures to detect potential exploitation attempts. The remediation process should also include updating related applications that depend on Xpdf for PDF processing to ensure complete protection against this class of memory corruption vulnerabilities.