CVE-2018-18455 in Xpdf
Summary
by MITRE
The GfxImageColorMap class in GfxState.cc in Xpdf 4.00 allows remote attackers to cause a denial of service (heap-based buffer over-read) via a crafted pdf file, as demonstrated by pdftoppm.
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Analysis
by VulDB Data Team • 03/07/2025
The vulnerability identified as CVE-2018-18455 represents a critical heap-based buffer over-read flaw within the GfxImageColorMap class of Xpdf version 4.00. This issue manifests specifically within the GfxState.cc source file and poses significant security risks to systems processing pdf documents. The vulnerability enables remote attackers to execute denial of service attacks by crafting malicious pdf files that trigger the buffer over-read condition when processed by applications utilizing the pdftoppm utility. The flaw demonstrates characteristics consistent with CWE-125, which describes out-of-bounds read vulnerabilities that occur when a program reads data beyond the boundaries of a buffer, potentially leading to unpredictable behavior and system instability. The attack vector leverages the PDF processing pipeline where crafted color mapping data within image objects causes the application to access memory locations beyond the allocated buffer space, resulting in a crash or system hang that constitutes a denial of service condition.
The technical exploitation of this vulnerability requires crafting a malicious pdf file containing specially constructed image color map data that triggers the buffer over-read during the processing phase. When pdftoppm or similar Xpdf-based applications attempt to render the problematic pdf document, the GfxImageColorMap class fails to properly validate the bounds of color mapping data, leading to memory access violations. This behavior aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1499.004 for network denial of service, as the vulnerability enables remote attackers to cause service disruption through crafted input. The heap-based nature of the buffer over-read indicates that the vulnerability occurs within dynamically allocated memory regions, making it particularly challenging to detect and prevent through static analysis alone. The flaw affects the core rendering functionality of Xpdf, which is widely used in various pdf processing applications and systems, amplifying the potential impact of successful exploitation.
The operational impact of CVE-2018-18455 extends beyond simple service disruption to encompass broader system reliability concerns for organizations relying on pdf processing capabilities. Systems that automatically process or convert pdf documents, including web applications, document management systems, and automated report generation tools, become vulnerable to this denial of service condition. The vulnerability can be exploited across multiple platforms where Xpdf is deployed, including servers, desktop applications, and cloud-based pdf processing services. Organizations utilizing Xpdf for pdf conversion, rendering, or analysis purposes face potential downtime and service interruptions when attackers successfully exploit this vulnerability through crafted pdf files. The remediation process requires updating to patched versions of Xpdf or implementing input validation measures to prevent processing of malformed pdf content, which may necessitate system downtime and application updates across affected environments.
Mitigation strategies for CVE-2018-18455 should focus on immediate patch application to Xpdf version 4.01 or later, which contains the necessary fixes for the buffer over-read vulnerability. System administrators should prioritize updating all affected applications and services that utilize Xpdf libraries, particularly those handling untrusted pdf input from external sources. Network-level defenses can include implementing pdf file validation filters that scan for known malicious patterns or suspicious color mapping structures before processing documents. Additionally, organizations should consider deploying sandboxing mechanisms for pdf processing to isolate potential exploitation attempts and prevent system-wide impact. The vulnerability demonstrates the importance of proper bounds checking and input validation in memory management operations, reinforcing principles from CWE-121 and CWE-125 that emphasize the need for robust buffer overflow protection measures. Regular security assessments and vulnerability scanning should include checks for outdated Xpdf installations to prevent exploitation of this and similar memory corruption vulnerabilities in the broader software ecosystem.