CVE-2016-6265 in MuPDF
Summary
by MITRE
Use-after-free vulnerability in the pdf_load_xref function in pdf/pdf-xref.c in MuPDF allows remote attackers to cause a denial of service (crash) via a crafted PDF file.
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Analysis
by VulDB Data Team • 09/20/2022
The CVE-2016-6265 vulnerability represents a critical use-after-free flaw within the MuPDF document processing library, specifically within the pdf_load_xref function located in pdf/pdf-xref.c. This vulnerability manifests when the library processes malformed PDF files, creating a scenario where memory that has been freed is subsequently accessed, leading to unpredictable behavior and system instability. The flaw occurs during the cross-reference table loading process, which is fundamental to PDF document parsing and memory management within the MuPDF framework. Attackers can exploit this weakness by crafting specially designed PDF documents that trigger the vulnerable code path, causing the application to crash or behave erratically.
The technical nature of this vulnerability aligns with CWE-416, which categorizes use-after-free conditions as a common class of memory safety issues. When the pdf_load_xref function encounters malformed cross-reference data, it may free memory resources that are subsequently accessed during the parsing of additional PDF elements. This memory management error creates an opportunity for remote attackers to manipulate the application's execution flow through carefully constructed input files. The vulnerability operates at the intersection of memory safety and input validation, where insufficient bounds checking and improper resource deallocation combine to create a dangerous condition. The flaw demonstrates a classic memory corruption vulnerability that can be exploited to achieve arbitrary code execution or denial of service, depending on the specific implementation and execution environment.
The operational impact of CVE-2016-6265 extends beyond simple denial of service, as it represents a fundamental security weakness in document processing software that is widely deployed across various platforms and applications. Systems utilizing MuPDF for PDF rendering, including web browsers, document viewers, and enterprise document management solutions, become vulnerable to remote exploitation. The vulnerability's remote attack surface means that simply opening a malicious PDF file can trigger the exploit, making it particularly dangerous in environments where users frequently encounter untrusted documents. This flaw directly impacts the integrity of PDF processing workflows and can be leveraged in phishing campaigns, malware distribution, or targeted attacks against organizations relying on MuPDF-based solutions. The vulnerability's exploitation requires minimal technical expertise, as the attack vector is simply opening a crafted PDF file, making it a preferred target for threat actors seeking broad impact.
Mitigation strategies for CVE-2016-6265 must address both immediate remediation and long-term architectural improvements in memory management practices. The most effective immediate solution involves applying the vendor-provided patch that corrects the memory deallocation and access patterns within the pdf_load_xref function. Organizations should implement comprehensive input validation and sanitization measures for all PDF processing workflows, ensuring that malformed or suspicious PDF content is properly handled before reaching vulnerable code paths. Additionally, deploying intrusion detection systems that can identify and block suspicious PDF file patterns can provide an additional layer of defense. The vulnerability underscores the importance of following secure coding practices such as those outlined in the CERT Secure Coding Standards, particularly guidelines related to memory management and resource handling. Regular security assessments and penetration testing of PDF processing components should be conducted to identify similar vulnerabilities in the broader codebase. Implementation of sandboxing techniques and privilege separation for PDF rendering processes can further reduce the potential impact of successful exploitation attempts, aligning with ATT&CK technique T1059 for defense against malicious code execution through process isolation.