CVE-2016-7950 in libXrender
Summary
by MITRE
The XRenderQueryFilters function in X.org libXrender before 0.9.10 allows remote X servers to trigger out-of-bounds write operations via vectors involving filter name lengths.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-7950 resides within the XRenderQueryFilters function of the X.org libXrender library version 0.9.9 and earlier. This issue represents a critical security flaw that enables remote attackers to manipulate X server connections and execute out-of-bounds write operations through carefully crafted filter name length parameters. The vulnerability manifests when the X server processes filter name length values that exceed expected boundaries, leading to memory corruption that can be exploited for arbitrary code execution or system compromise.
The technical implementation of this vulnerability stems from inadequate input validation within the XRenderQueryFilters function. When a remote X server sends filter name length information, the libXrender library fails to properly bounds-check these values before using them to allocate memory or perform memory operations. This allows an attacker to provide malicious length parameters that cause the library to write data beyond the allocated memory boundaries, potentially overwriting adjacent memory regions with controlled data. The flaw operates at the protocol level where X server implementations handle rendering filter queries, making it particularly dangerous in networked environments where remote X servers can connect and send crafted requests.
The operational impact of CVE-2016-7950 extends beyond simple memory corruption, as it can be leveraged to achieve remote code execution on systems running vulnerable X server implementations. Attackers can exploit this vulnerability to inject malicious code into the X server process memory, potentially escalating privileges or gaining full control over the affected system. The vulnerability affects any system running X.org libXrender version 0.9.9 or earlier, including various Linux distributions and Unix-like systems that utilize the X Window System for graphical user interfaces. The attack vector requires network connectivity to the X server and the ability to establish an X protocol connection, making it particularly concerning for servers that expose X11 services to untrusted networks or the internet.
Mitigation strategies for CVE-2016-7950 primarily focus on upgrading the affected libXrender library to version 0.9.10 or later, which includes patches that properly validate filter name length parameters and prevent out-of-bounds memory operations. System administrators should also implement network segmentation to limit access to X server services, disable unnecessary X11 forwarding capabilities, and employ firewall rules to restrict X server connections to trusted hosts only. Additionally, organizations should consider implementing intrusion detection systems that can identify suspicious X protocol traffic patterns and monitor for potential exploitation attempts. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of how improper input validation can lead to memory corruption vulnerabilities. From an ATT&CK perspective, this vulnerability maps to T1059.007 for remote code execution capabilities and T1566 for initial access through network services, making it a significant threat in enterprise security environments where X server services remain exposed to external networks.