CVE-2016-7944 in libXfixes
Summary
by MITRE
Integer overflow in X.org libXfixes before 5.0.3 on 32-bit platforms might allow remote X servers to gain privileges via a length value of INT_MAX, which triggers the client to stop reading data and get out of sync.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-7944 represents a critical integer overflow flaw within the X.org libXfixes library version 5.0.2 and earlier on 32-bit platforms. This issue stems from inadequate input validation when processing length values in X protocol communication, creating a scenario where remote X servers can exploit the system through carefully crafted malicious data sequences. The flaw specifically manifests when an attacker sends a length value equal to INT_MAX, which represents the maximum value an integer can hold on 32-bit systems. This particular value triggers a condition where the client application ceases to read incoming data streams and becomes desynchronized from the server communication protocol.
The technical exploitation of this vulnerability occurs through the manipulation of X protocol packet lengths within the libXfixes library implementation. When the library processes a packet with a length field set to INT_MAX, the integer overflow causes the system to misinterpret the data flow, leading to a state where the client stops reading data from the network connection. This desynchronization creates a window of opportunity for attackers to inject additional malicious commands or manipulate the communication sequence. The vulnerability is particularly dangerous because it operates at the protocol level, allowing attackers to potentially escalate privileges or execute arbitrary code on systems running affected versions of the X.org library.
From an operational perspective, this vulnerability poses significant risks to systems relying on X Window System for graphical user interfaces, particularly in environments where remote access is permitted. The impact extends beyond simple privilege escalation to potentially enable complete system compromise, as the desynchronization can be exploited to bypass security mechanisms and execute unauthorized operations. The vulnerability affects any system running 32-bit versions of X.org libXfixes prior to version 5.0.3, making it particularly relevant for older systems and embedded devices that may not have received timely updates. Network-based attacks can be executed without requiring local access, making the vulnerability particularly dangerous in multi-user or public computing environments.
The mitigation strategy for CVE-2016-7944 centers on updating to X.org libXfixes version 5.0.3 or later, which includes proper bounds checking and integer overflow protection mechanisms. Organizations should prioritize patching affected systems, particularly those handling remote X connections or operating in networked environments. Additional defensive measures include implementing network segmentation to limit X server access, disabling unnecessary X11 forwarding capabilities, and monitoring for suspicious X protocol activity. This vulnerability aligns with CWE-190, which categorizes integer overflow conditions, and can be mapped to ATT&CK technique T1068, which covers local privilege escalation through system weaknesses. System administrators should also consider implementing intrusion detection systems to monitor for exploitation attempts and maintain comprehensive audit logs of X server communications to detect potential abuse of this vulnerability.