CVE-2018-16648 in MuPDF
Summary
by MITRE
In Artifex MuPDF 1.13.0, the fz_append_byte function in fitz/buffer.c allows remote attackers to cause a denial of service (segmentation fault) via a crafted pdf file. This is caused by a pdf/pdf-device.c pdf_dev_alpha array-index underflow.
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Analysis
by VulDB Data Team • 09/12/2024
The vulnerability identified as CVE-2018-16648 represents a critical denial of service flaw within Artifex MuPDF version 1.13.0, specifically affecting the fz_append_byte function located in fitz/buffer.c. This weakness manifests when processing maliciously crafted pdf files, creating a scenario where remote attackers can trigger system crashes through segmentation faults. The underlying cause stems from an array-index underflow condition within the pdf/pdf-device.c component, specifically involving the pdf_dev_alpha array. This type of vulnerability falls under the category of software defects that can be exploited without authentication, making it particularly dangerous in environments where pdf processing occurs automatically or through untrusted input sources.
The technical implementation of this flaw demonstrates a classic buffer management error where the pdf_dev_alpha array receives an invalid index value during processing of pdf content. When MuPDF attempts to append bytes to a buffer during rendering operations, the improper handling of alpha channel data causes the array index to underflow, resulting in memory access violations that manifest as segmentation faults. This vulnerability is particularly concerning because it operates at the core rendering layer of the pdf processing engine, meaning any application or system utilizing MuPDF for pdf document handling could be affected. The flaw does not appear to enable arbitrary code execution or data leakage, but rather focuses on system availability through controlled crash conditions that can be repeatedly triggered by malicious actors.
The operational impact of CVE-2018-16648 extends beyond simple system crashes, as it can be leveraged to create persistent denial of service conditions against applications relying on MuPDF for pdf processing. This vulnerability affects systems where pdf documents are automatically processed or rendered without proper input validation, including web applications, document management systems, and pdf viewers that incorporate MuPDF as a backend library. Attackers can craft specific pdf files that when opened or processed by vulnerable systems will cause immediate system instability, potentially leading to service disruption for legitimate users and creating opportunities for more sophisticated attacks. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and demonstrates how seemingly minor implementation flaws can result in significant operational consequences. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, where adversaries exploit software flaws to disrupt services.
Mitigation strategies for CVE-2018-16648 primarily involve upgrading to patched versions of MuPDF where the array index validation has been corrected. System administrators should prioritize updating their MuPDF installations to versions that address this specific underflow condition in the pdf_dev_alpha array handling. Additionally, implementing input validation measures such as pdf file sanitization, content scanning, and limiting pdf processing to trusted sources can provide defense-in-depth measures. Organizations should also consider implementing monitoring and alerting for unusual system crashes or segmentation faults that may indicate exploitation attempts. The vulnerability underscores the importance of regular security updates and proper input validation practices in preventing remote code execution and denial of service attacks. Security teams should also conduct vulnerability assessments to identify systems running affected versions of MuPDF and ensure comprehensive patch management protocols are in place to prevent similar issues from arising in other components of their software ecosystems.