CVE-2018-7174 in Xpdf
Summary
by MITRE
An issue was discovered in xpdf 4.00. An infinite loop in XRef::Xref allows an attacker to cause denial of service because loop detection exists only for tables, not streams.
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Analysis
by VulDB Data Team • 03/07/2025
The vulnerability identified as CVE-2018-7174 resides within the xpdf 4.00 document processing library, specifically affecting the XRef::Xref component responsible for handling cross-reference tables in pdf files. This flaw represents a critical denial of service condition that can be exploited by malicious actors to disrupt system operations through carefully crafted pdf documents. The vulnerability stems from an insufficient loop detection mechanism within the xpdf library's parsing logic, creating a scenario where the application enters an infinite loop when processing malformed pdf files containing specific cross-reference structures.
The technical implementation of this vulnerability involves the XRef::Xref class failing to properly detect looping references within pdf stream objects, while maintaining loop detection only for table structures. This asymmetry in loop detection creates a condition where pdf files containing circular references within stream data can cause the parser to continuously iterate through the same data structures without termination. The flaw demonstrates poor defensive programming practices where the library assumes that all cross-reference data will follow predictable patterns, failing to implement comprehensive loop detection across all data types within the pdf structure.
From an operational perspective, this vulnerability poses significant risks to systems that process pdf documents automatically, including email servers, document management systems, web applications, and security scanning tools. The infinite loop condition can consume excessive cpu cycles and memory resources, effectively rendering the affected system unavailable to legitimate users. Attackers can exploit this vulnerability by simply sending a specially crafted pdf file to any system running xpdf 4.00, causing the application to hang indefinitely and potentially leading to resource exhaustion. The impact extends beyond simple denial of service as it can affect multiple concurrent processes and potentially allow for resource exhaustion attacks that can compromise entire server environments.
The vulnerability aligns with CWE-835, which addresses loop termination issues in software implementations, and demonstrates characteristics consistent with ATT&CK technique T1499.004, focusing on network denial of service attacks through resource exhaustion. Organizations using xpdf 4.00 should immediately implement mitigations including updating to patched versions of the library, implementing input validation and sanitization for pdf files, and deploying rate limiting mechanisms to prevent abuse of vulnerable systems. Additionally, network segmentation and monitoring solutions should be employed to detect unusual resource consumption patterns that may indicate exploitation attempts. The recommended remediation includes upgrading to xpdf version 4.01 or later where the loop detection has been enhanced to cover both table and stream structures, ensuring comprehensive protection against this specific denial of service vulnerability.