CVE-2003-0581 in X Fontserver for Truetype Fonts
Summary
by MITRE
X Fontserver for Truetype fonts (xfstt) 1.4 allows remote attackers to cause a denial of service and possibly execute arbitrary code via a (1) FS_QueryXExtents8 or (2) FS_QueryXBitmaps8 packet, and possibly other types of packets, with a large num_ranges value, which causes an out-of-bounds array access.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/11/2019
The vulnerability identified as CVE-2003-0581 affects the X Fontserver for Truetype fonts (xfstt) version 1.4, representing a critical security flaw that exposes systems to both denial of service attacks and potential remote code execution. This vulnerability resides within the font server implementation that handles Truetype font rendering in X Window System environments, where the server processes font-related packets from remote clients. The flaw specifically manifests when the server receives malformed packets containing excessive num_ranges values, leading to improper memory handling and array bounds violations.
The technical root cause of this vulnerability stems from insufficient input validation within the font server's packet processing logic. When the xfstt server receives FS_QueryXExtents8 or FS_QueryXBitmaps8 packets with oversized num_ranges parameters, it fails to properly validate the range values before attempting array access operations. This deficiency creates a classic out-of-bounds memory access condition that can be exploited by remote attackers to manipulate memory layout and potentially execute arbitrary code. The vulnerability operates at the protocol level, making it particularly dangerous as it can be triggered through standard network communication without requiring local system access.
The operational impact of CVE-2003-0581 extends beyond simple service disruption to encompass potential system compromise and unauthorized code execution. Remote attackers can leverage this vulnerability to cause the font server process to crash, resulting in denial of service for legitimate users who require font rendering capabilities. More critically, the out-of-bounds array access condition may allow attackers to overwrite critical memory locations, potentially enabling arbitrary code execution with the privileges of the font server process. This could lead to complete system compromise, especially when the font server runs with elevated privileges or is part of a larger system architecture.
The vulnerability aligns with CWE-129, which describes improper validation of array index values, and represents a specific instance of improper input validation that leads to memory corruption. From an ATT&CK framework perspective, this vulnerability maps to T1190 - Exploit Public-Facing Application, where attackers target exposed services to gain initial access. The attack surface is particularly concerning in environments where font servers are exposed to untrusted networks, as the vulnerability can be exploited without authentication or specialized tools. Organizations using xfstt version 1.4 should immediately implement mitigations including patching to newer versions, network segmentation to isolate font servers, and implementing firewall rules to restrict access to font server ports.
Security practitioners should note that this vulnerability demonstrates the importance of robust input validation in network-facing applications, particularly those handling multimedia content like fonts. The flaw highlights the need for comprehensive memory safety practices including bounds checking, array validation, and proper error handling in protocol implementations. The vulnerability also underscores the risks associated with legacy font server implementations that may not have undergone modern security reviews. Mitigation strategies should include immediate patch deployment, network monitoring for exploitation attempts, and implementation of intrusion detection systems to identify potential exploitation of similar vulnerabilities in other font rendering components. Organizations should also consider implementing network access controls to limit who can connect to font server services and regularly audit their font server configurations to ensure they are not unnecessarily exposed to external networks.