CVE-2011-5244 in t1lib
Summary
by MITRE
Multiple off-by-one errors in the (1) token and (2) linetoken functions in backend/dvi/mdvi-lib/afmparse.c in t1lib, as used in teTeX 3.0.x, GNOME evince, and possibly other products, allow remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via a DVI file containing a crafted Adobe Font Metrics (AFM) file, different vulnerabilities than CVE-2010-2642 and CVE-2011-0433.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2011-5244 represents a critical security flaw within the t1lib library that affects multiple applications including teTeX 3.0.x and GNOME evince. This issue stems from off-by-one errors in the token and linetoken functions located in the backend/dvi/mdvi-lib/afmparse.c file, which processes Adobe Font Metrics files during DVI document rendering. The vulnerability specifically targets the parsing mechanism that handles AFM files, which are essential components for proper font rendering in document processing systems. These off-by-one errors occur when the functions fail to properly validate array bounds during string parsing operations, creating opportunities for memory corruption that can lead to system instability.
The technical implementation of this vulnerability involves buffer overflow conditions that manifest when processing malformed AFM files embedded within DVI documents. When the token and linetoken functions encounter crafted input data, they increment counters or indices beyond their intended boundaries, potentially causing memory corruption that results in program termination or unpredictable behavior. The vulnerability is particularly dangerous because it can be triggered through normal document processing operations, making it exploitable via remote attack vectors. The flaw allows attackers to craft malicious DVI files containing specially formatted AFM data that, when processed by vulnerable applications, causes the parsing functions to access memory locations outside their allocated buffers, leading to crashes or potential code execution.
From an operational perspective, this vulnerability presents significant risks to document processing systems that rely on t1lib for font handling. Applications such as GNOME evince and teTeX 3.0.x become susceptible to denial of service attacks when processing untrusted DVI documents, as the parsing functions will crash upon encountering malformed AFM data. The potential for arbitrary code execution adds an additional layer of threat, as attackers could leverage this vulnerability to gain unauthorized access to systems processing these documents. The impact extends beyond individual application crashes to potentially compromise entire document processing workflows in environments where automated document handling is common. This vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and aligns with ATT&CK technique T1203 for "Exploitation for Client Execution" when considering the remote code execution potential.
The exploitation of CVE-2011-5244 requires minimal privileges and can be accomplished through the simple delivery of a malicious DVI file containing crafted AFM data. Attackers can create documents that trigger the off-by-one errors during normal document rendering operations, making this vulnerability particularly dangerous in environments where users might encounter untrusted documents. The vulnerability affects multiple products due to the widespread use of t1lib in various document processing applications, amplifying the potential impact. Security practitioners should note that the vulnerability differs from related issues CVE-2010-2642 and CVE-2011-0433, indicating that similar but distinct flaws exist in the same codebase. Mitigation strategies should focus on updating to patched versions of affected applications, implementing input validation for DVI and AFM file processing, and deploying network-based intrusion detection systems to monitor for suspicious file processing activities. Additionally, organizations should consider implementing sandboxing mechanisms for document processing to limit potential damage from successful exploitation attempts.