CVE-2011-1552 in Xpdf
Summary
by MITRE
t1lib 5.1.2 and earlier, as used in Xpdf before 3.02pl6, teTeX, and other products, reads from invalid memory locations, which allows remote attackers to cause a denial of service (application crash) via a crafted Type 1 font in a PDF document, a different vulnerability than CVE-2011-0764.
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Analysis
by VulDB Data Team • 12/28/2024
The vulnerability identified as CVE-2011-1552 represents a critical memory access flaw affecting t1lib version 5.1.2 and earlier implementations within various PDF rendering systems including Xpdf before version 3.02pl6 and teTeX. This issue stems from improper handling of invalid memory locations during Type 1 font processing within PDF documents, creating a remote attack vector that can be exploited by malicious actors to disrupt system operations. The flaw specifically manifests when applications attempt to process malformed Type 1 font data, leading to unauthorized memory access patterns that result in application crashes and subsequent denial of service conditions.
The technical implementation of this vulnerability involves the improper validation of font data structures within the t1lib library, which serves as a foundational component for Type 1 font handling in numerous document processing applications. When a PDF document contains a specially crafted Type 1 font with malformed memory references, the library attempts to access memory locations that have not been properly allocated or initialized. This memory access violation occurs during the font rendering process, where the application's memory management mechanisms fail to properly sanitize input data before attempting to dereference pointers to invalid memory regions. The vulnerability falls under the category of memory corruption issues, specifically addressing improper access to memory locations that should have been validated or rejected during the parsing phase.
From an operational impact perspective, this vulnerability creates significant security concerns for organizations relying on PDF rendering capabilities, as remote attackers can exploit this weakness to cause denial of service attacks against systems processing PDF documents. The attack requires minimal privileges and can be executed through the simple act of opening a malicious PDF document containing the crafted Type 1 font, making it particularly dangerous in environments where users frequently open untrusted documents. The vulnerability specifically affects applications that utilize t1lib for font handling, including but not limited to Xpdf, teTeX, and various other PDF processing tools that depend on this library for proper document rendering functionality.
The exploitation of CVE-2011-1552 aligns with ATT&CK technique T1203, which describes exploitation of software vulnerabilities for denial of service purposes, and demonstrates the importance of proper input validation and memory management practices in security-critical applications. This vulnerability is categorized under CWE-125, which addresses out-of-bounds read conditions, and CWE-248, which covers improper exception handling. Organizations should implement immediate mitigations including updating to patched versions of affected software, implementing proper input validation for font data, and deploying network segmentation to limit exposure. Additionally, security teams should consider implementing application whitelisting policies and regular vulnerability assessments to prevent exploitation of similar memory access vulnerabilities that may exist in other components of their document processing infrastructure.
The remediation strategy for this vulnerability requires comprehensive patch management across all affected systems, with particular attention to updating the t1lib library to versions that properly validate font data structures before attempting memory access operations. System administrators should also consider implementing additional security controls such as sandboxing PDF rendering processes, restricting font handling capabilities in web browsers, and monitoring for suspicious PDF document access patterns. Organizations utilizing legacy systems that cannot be immediately updated should consider implementing network-level controls to prevent access to potentially malicious PDF documents and establish incident response procedures to address potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper memory management and input validation in preventing remote code execution and denial of service attacks in document processing applications.