CVE-2011-0764 in Xpdf
Summary
by MITRE
t1lib 5.1.2 and earlier, as used in Xpdf before 3.02pl6, teTeX, and other products, uses an invalid pointer in conjunction with a dereference operation, which allows remote attackers to execute arbitrary code via a crafted Type 1 font in a PDF document, as demonstrated by testz.2184122398.pdf.
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Analysis
by VulDB Data Team • 12/28/2024
The vulnerability identified as CVE-2011-0764 represents a critical memory corruption flaw affecting t1lib version 5.1.2 and earlier implementations within PDF processing software ecosystems. This vulnerability specifically impacts Xpdf before version 3.02pl6, teTeX, and numerous other products that rely on t1lib for Type 1 font handling. The flaw manifests when processing maliciously crafted Type 1 fonts embedded within PDF documents, creating a scenario where invalid memory pointers are utilized in conjunction with dereference operations. This particular combination creates a predictable memory access violation that adversaries can exploit to execute arbitrary code on affected systems. The vulnerability was demonstrated through the testz.2184122398.pdf file, which served as a proof-of-concept payload designed to trigger the memory corruption during font rendering operations.
The technical exploitation of this vulnerability occurs during the processing of Type 1 font data within PDF documents, where t1lib's font handling code fails to properly validate memory pointer states before dereferencing them. This memory safety issue directly maps to CWE-476, which describes NULL pointer dereference conditions that can lead to arbitrary code execution. When a malicious PDF document containing a specially crafted Type 1 font is processed by vulnerable software, the t1lib library attempts to access memory locations that have either been freed or never properly allocated. The improper pointer handling creates a condition where attackers can manipulate the memory layout to redirect execution flow, effectively allowing remote code execution without requiring local system access. This vulnerability operates at the intersection of memory management flaws and code execution hijacking techniques that align with ATT&CK technique T1059.007 for command and scripting interpreter.
The operational impact of CVE-2011-0764 extends beyond simple code execution capabilities, as it represents a significant threat vector for remote exploitation in environments where PDF documents are frequently processed. Organizations utilizing vulnerable versions of Xpdf, teTeX, or any software stack incorporating t1lib 5.1.2 or earlier face substantial risk from this vulnerability, particularly in scenarios involving email attachments, web-based PDF viewers, or document processing systems. The remote exploitation capability means that adversaries can deliver malicious payloads through standard PDF document distribution channels without requiring user interaction beyond opening the document. This vulnerability particularly affects enterprise environments where PDF processing is common, including document management systems, web applications, and security scanning tools that process untrusted PDF content. The lack of input validation in the font processing pipeline creates an attack surface that can be leveraged for privilege escalation, data exfiltration, or further network compromise.
Mitigation strategies for CVE-2011-0764 require immediate remediation through software version updates and implementation of defensive measures. The primary solution involves upgrading to t1lib version 5.1.3 or later, which contains patches addressing the invalid pointer dereference issue, along with updating affected software stacks such as Xpdf to version 3.02pl6 or newer. Organizations should implement comprehensive patch management policies that prioritize updates to font processing libraries and PDF rendering engines. Additional defensive measures include implementing strict input validation for PDF documents, deploying sandboxed environments for PDF processing, and configuring web applications to filter or reject PDF documents containing suspicious font elements. Network-based mitigations such as content filtering and web application firewalls can help prevent exploitation attempts by blocking known malicious PDF files. Security monitoring should focus on detecting unusual PDF processing patterns and potential exploitation attempts, while incident response procedures should include immediate containment and forensic analysis capabilities to address successful exploitation attempts.