CVE-2017-17858 in MuPDF
Summary
by MITRE
Heap-based buffer overflow in the ensure_solid_xref function in pdf/pdf-xref.c in Artifex MuPDF 1.12.0 allows a remote attacker to potentially execute arbitrary code via a crafted PDF file, because xref subsection object numbers are unrestricted.
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Analysis
by VulDB Data Team • 02/02/2023
The heap-based buffer overflow vulnerability identified as CVE-2017-17858 resides within the Artifex MuPDF library version 1.12.0, specifically in the pdf/pdf-xref.c module within the ensure_solid_xref function. This flaw represents a critical security weakness that enables remote code execution when processing maliciously crafted PDF files. The vulnerability stems from insufficient validation of xref subsection object numbers, which creates an exploitable condition where attacker-controlled data can overwrite adjacent memory locations in the heap. The underlying issue manifests when the PDF parser encounters malformed cross-reference (xref) sections that contain unrestricted object number values, allowing an attacker to manipulate memory layout and potentially execute arbitrary code with the privileges of the vulnerable application.
This vulnerability directly maps to CWE-121, heap-based buffer overflow, and aligns with ATT&CK technique T1203, Exploitation for Client Execution, as it enables remote attackers to execute malicious code through PDF document manipulation. The flaw operates by leveraging the PDF file format's cross-reference structure, which is used to track object locations within the document. When the ensure_solid_xref function processes these references without proper bounds checking on object numbers, it fails to validate that the referenced object indices remain within acceptable memory boundaries. This validation gap permits attackers to craft PDF files containing malicious xref subsection entries that cause buffer overflows during memory allocation and data copying operations.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass potential system compromise and data breaches. Attackers can exploit this weakness by embedding specially crafted PDF files in phishing campaigns, malicious websites, or email attachments, making it particularly dangerous in enterprise environments where PDF processing is common. The vulnerability affects any application that utilizes Artifex MuPDF for PDF rendering or processing, including web browsers, document viewers, and content management systems. Successful exploitation could lead to complete system compromise, data exfiltration, or persistent backdoor installation, depending on the target environment and execution context.
Mitigation strategies for CVE-2017-17858 should prioritize immediate patching of affected MuPDF versions to 1.13.0 or later, where the vulnerability has been addressed through proper bounds checking of xref subsection object numbers. Organizations should implement network-level defenses including PDF file filtering and sandboxing mechanisms to prevent execution of potentially malicious documents. Additionally, security configurations should enforce strict input validation for all PDF processing pipelines and maintain regular vulnerability assessments to identify similar issues in other PDF libraries. The fix implemented by Artifex involves adding comprehensive validation checks that ensure xref object numbers remain within expected ranges before processing, effectively preventing the heap overflow condition from occurring.