CVE-2017-13722 in libXfont
Summary
by MITRE
In the pcfGetProperties function in bitmap/pcfread.c in libXfont through 1.5.2 and 2.x before 2.0.2, a missing boundary check (for PCF files) could be used by local attackers authenticated to an Xserver for a buffer over-read, for information disclosure or a crash of the X server.
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Analysis
by VulDB Data Team • 01/03/2023
The vulnerability identified as CVE-2017-13722 represents a critical buffer over-read flaw within the libXfont library, specifically affecting the pcfGetProperties function in bitmap/pcfread.c. This issue exists in versions through 1.5.2 and 2.x before 2.0.2, creating a significant security risk for systems utilizing X Window System implementations. The flaw stems from inadequate input validation mechanisms that fail to properly verify boundary conditions when processing PCF (Portable Compiled Format) font files, which are commonly used within X server environments for font rendering and display operations.
The technical implementation of this vulnerability allows local attackers who already possess authentication credentials to an X server to manipulate PCF font files in ways that trigger buffer over-read conditions. When the pcfGetProperties function processes malformed or specially crafted PCF files, the absence of proper boundary checks causes the program to read data beyond the allocated memory buffer. This memory corruption can manifest in multiple ways including information disclosure through memory contents being inadvertently exposed, system crashes causing denial of service conditions, or potentially more severe exploitation vectors depending on the specific memory layout and system configuration. The vulnerability specifically targets the PCF file format processing within the X font subsystem, making it particularly relevant to Unix-like systems running X Window servers.
The operational impact of CVE-2017-13722 extends beyond simple crash conditions to potentially enable information disclosure attacks that could reveal sensitive memory contents including cryptographic keys, user credentials, or other confidential data stored in memory. This makes the vulnerability particularly dangerous in multi-user environments where local attackers might leverage their authenticated access to gain additional privileges or extract valuable information from the X server process. The flaw affects the fundamental font processing capabilities of X servers, potentially disrupting graphical user interfaces and rendering systems that depend on proper font handling. Systems running affected versions of libXfont are at risk of experiencing service disruption, unauthorized information access, and potential escalation of privileges through memory corruption exploitation techniques.
Mitigation strategies for this vulnerability require immediate patching of affected libXfont installations to versions 1.5.2 or 2.0.2 and later, which contain the necessary boundary check implementations to prevent the over-read conditions. System administrators should also implement additional security measures including restricting local access to X servers where possible, monitoring for unusual font file processing activities, and ensuring proper access controls are in place for X server resources. The vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and can be mapped to ATT&CK technique T1068, which involves exploiting local privileges to gain system access. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts. Regular security audits of X server configurations and font processing components should be conducted to identify and remediate similar boundary condition vulnerabilities that may exist in other system components.