CVE-2017-16611 in libXfont
Summary
by MITRE
In libXfont before 1.5.4 and libXfont2 before 2.0.3, a local attacker can open (but not read) files on the system as root, triggering tape rewinds, watchdogs, or similar mechanisms that can be triggered by opening files.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/16/2023
The vulnerability identified as CVE-2017-16611 affects the X Window System font handling libraries libXfont and libXfont2, specifically versions prior to 1.5.4 and 2.0.3 respectively. This issue represents a privilege escalation vulnerability that allows local attackers to open system files with root privileges through the font processing mechanisms. The flaw stems from improper file access controls within the font loading and processing functions of these libraries. When applications or services process font files, they utilize these libraries to handle font data, creating an opportunity for malicious actors to exploit the vulnerability by crafting specially formatted font files that trigger unintended file access patterns.
The technical implementation of this vulnerability involves the manipulation of font file processing within the X11 font subsystem. When libXfont or libXfont2 encounters font files, particularly those with malformed or specially crafted content, the libraries may attempt to open additional system files during the font processing pipeline. This occurs because the font handling code does not properly validate or restrict file access paths during font processing operations. The vulnerability specifically affects the way these libraries handle font file metadata and font data structures, allowing attackers to influence the underlying file access mechanisms to open arbitrary files with elevated privileges.
The operational impact of this vulnerability extends beyond simple file access, as it can trigger critical system mechanisms that are typically protected from unauthorized access. When the vulnerable libraries open files during font processing, they may inadvertently activate hardware-level systems such as tape drives requiring rewind operations, watchdog timers, or other system components that respond to file access events. This creates a potential for system disruption, resource exhaustion, or even physical damage to hardware components that respond to these specific file access patterns. The vulnerability essentially transforms normal font processing operations into potential attack vectors that can manipulate system-level hardware and services.
From a cybersecurity perspective, this vulnerability aligns with CWE-264, which covers permissions, privileges, and access control issues in software systems. The flaw demonstrates poor privilege separation and inadequate input validation within the font processing pipeline. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically within the T1068 - Exploitation for Privilege Escalation tactic. Attackers can leverage this vulnerability to gain unauthorized access to system resources and potentially escalate their privileges to root level access. The local nature of the attack means that exploitation requires only user-level access to the system, making it particularly concerning for multi-user environments where attackers might already have legitimate access to system resources.
The recommended mitigations for this vulnerability include immediate upgrade of libXfont and libXfont2 libraries to versions 1.5.4 and 2.0.3 respectively, which contain patches addressing the improper file access controls. System administrators should also implement monitoring of font processing operations and file access patterns to detect potential exploitation attempts. Additionally, organizations should consider implementing additional security controls such as restricting font processing capabilities for untrusted applications and implementing proper privilege separation in font handling services. The vulnerability highlights the importance of proper input validation and privilege management in system libraries, particularly those that handle user-provided data in critical system components.