CVE-2018-8104 in Xpdf
Summary
by MITRE
The BufStream::lookChar function in Stream.cc in xpdf 4.00 allows attackers to launch denial of service (heap-based buffer over-read and application crash) via a specific pdf file, as demonstrated by pdftohtml.
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Analysis
by VulDB Data Team • 03/07/2025
The vulnerability identified as CVE-2018-8104 resides within the xpdf library's Stream.cc file, specifically in the BufStream::lookChar function. This flaw represents a classic heap-based buffer over-read condition that occurs when processing malformed pdf files. The vulnerability is particularly concerning because it can be exploited through legitimate pdf processing tools such as pdftohtml, making it accessible to attackers who might craft malicious pdf documents to trigger the condition. The xpdf library serves as a foundational component for numerous pdf processing applications, including various pdf viewers, converters, and document management systems, amplifying the potential impact of this vulnerability.
The technical mechanism behind this vulnerability involves improper bounds checking within the BufStream::lookChar function. When the function attempts to read characters from a buffer stream without adequate validation of buffer boundaries, it can access memory locations beyond the allocated buffer space. This heap-based buffer over-read occurs during the processing of specific pdf file structures that manipulate the stream reading logic in unexpected ways. The flaw manifests as a memory access violation that results in application instability and subsequent crashes. According to CWE standards, this vulnerability maps directly to CWE-125: "Out-of-bounds Read," which describes situations where programs read data past the end of a buffer, potentially exposing sensitive memory contents or causing application termination.
The operational impact of CVE-2018-8104 extends beyond simple application crashes to represent a significant denial of service threat. When exploited, this vulnerability can cause pdf processing applications to terminate unexpectedly, disrupting legitimate document workflows and potentially providing attackers with a means to disrupt services. The vulnerability is particularly dangerous in automated processing environments where pdf files are processed in bulk, as a single malicious document could cause cascading failures across multiple systems. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving resource exhaustion and service disruption, though it does not directly enable privilege escalation or data exfiltration. The exploitability is relatively straightforward since it only requires crafting a specific pdf file structure that triggers the buffer over-read condition.
Mitigation strategies for CVE-2018-8104 should focus on both immediate remediation and long-term defensive measures. The primary solution involves upgrading to a patched version of xpdf that addresses the buffer over-read condition in the BufStream::lookChar function. Organizations should also implement input validation measures that sanitize pdf files before processing, including implementing proper bounds checking and memory access controls. Additionally, deploying application sandboxing techniques can limit the impact of successful exploitation attempts. Security monitoring should include detection of unusual application crash patterns and memory access violations that might indicate exploitation attempts. Network-level defenses can also be implemented to filter suspicious pdf file content, particularly in environments where pdf processing is automated or exposed to untrusted inputs. The vulnerability underscores the importance of maintaining up-to-date software libraries and implementing robust memory safety practices in document processing applications.