CVE-2013-1983 in libXfixes
Summary
by MITRE
Integer overflow in X.org libXfixes 5.0 and earlier allows X servers to trigger allocation of insufficient memory and a buffer overflow via vectors related to the XFixesGetCursorImage function.
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Analysis
by VulDB Data Team • 05/14/2021
The vulnerability identified as CVE-2013-1983 represents a critical integer overflow flaw within the X.org libXfixes library version 5.0 and earlier implementations. This issue specifically affects the XFixesGetCursorImage function which is responsible for retrieving cursor image data from X servers. The flaw arises from improper input validation and arithmetic handling when processing cursor image dimensions and memory allocation parameters. The vulnerability operates at the intersection of buffer management and integer arithmetic, creating a scenario where malicious X server implementations can manipulate the system's memory allocation behavior through crafted cursor image requests.
The technical exploitation of this vulnerability stems from the library's failure to properly validate integer values when calculating buffer sizes for cursor image data structures. When an X server sends a cursor image request with maliciously crafted dimensions, the integer overflow occurs during the arithmetic operations used to determine the required memory allocation size. This overflow results in a situation where the system allocates insufficient memory for the buffer, creating a condition where subsequent memory writes exceed the allocated bounds. The vulnerability is classified under CWE-190 as an integer overflow, specifically involving signed integer overflow that leads to memory corruption and potential arbitrary code execution.
The operational impact of CVE-2013-1983 extends beyond simple memory corruption, as it provides a pathway for remote attackers to potentially execute arbitrary code on systems running affected X.org implementations. This vulnerability affects the core X Window System infrastructure, which serves as the foundation for graphical user interfaces across numerous Unix-like operating systems including various Linux distributions and BSD implementations. The attack vector is particularly concerning because it can be triggered through legitimate X server communication protocols, making it difficult to distinguish between malicious and benign requests at the network level. The vulnerability creates a persistent risk for systems that rely on X11 forwarding, remote desktop implementations, and graphical server environments where untrusted X servers might be present.
Mitigation strategies for this vulnerability require immediate patching of the libXfixes library to version 5.1 or later, where the integer overflow has been addressed through proper input validation and arithmetic bounds checking. System administrators should also implement network segmentation and access controls to limit exposure of X server implementations to untrusted networks or users. The remediation process must include comprehensive testing of X server configurations and applications that depend on cursor image functionality to ensure that the patched library operates correctly without introducing regressions. Security monitoring should be enhanced to detect anomalous X server behavior patterns that might indicate exploitation attempts, particularly around cursor image requests and memory allocation patterns. This vulnerability aligns with ATT&CK technique T1059.007 for command and script injection through X11 protocols and demonstrates the importance of maintaining up-to-date graphics subsystem components in enterprise security postures. Organizations should also consider implementing additional defensive measures such as mandatory access controls and privilege separation for X server processes to limit the potential damage from successful exploitation attempts.