CVE-2017-9722 in Android
Summary
by MITRE
In Android for MSM, Firefox OS for MSM, QRD Android, with all Android releases from CAF using the Linux kernel, when updating custom EDID (hdmi_tx_sysfs_wta_edid), if edid_size, which is controlled by userspace, is too large, a buffer overflow occurs.
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Analysis
by VulDB Data Team • 12/21/2019
The vulnerability described in CVE-2017-9722 represents a critical buffer overflow condition affecting multiple Android variants including MSM, Firefox OS, and QRD Android platforms that utilize the Linux kernel. This flaw manifests specifically during the process of updating custom EDID (Extended Display Identification Data) information through the hdmi_tx_sysfs_wta_edid interface, where the system fails to properly validate input parameters from userspace applications. The buffer overflow occurs when the edid_size parameter, which is entirely controlled by untrusted userspace code, exceeds the allocated buffer boundaries within the kernel space. This vulnerability resides in the HDMI transmitter subsystem and demonstrates a classic case of improper input validation where kernel-level memory management fails to account for potentially malicious or malformed input data.
The technical exploitation of this vulnerability occurs through a privilege escalation vector where a malicious userspace application can manipulate the edid_size parameter to exceed the intended buffer limits. When the kernel processes this oversized parameter, it writes beyond the allocated memory space, potentially overwriting adjacent kernel memory structures, function pointers, or other critical data elements. The vulnerability specifically targets the Linux kernel's HDMI subsystem implementation, where the hdmi_tx_sysfs_wta_edid interface serves as the attack surface for manipulating display identification data. This interface is designed to allow userspace applications to update EDID information for HDMI output devices, but the lack of proper bounds checking creates an exploitable condition. The flaw directly maps to CWE-121, which describes heap-based buffer overflow conditions, and represents a variant of the broader class of memory corruption vulnerabilities that can lead to arbitrary code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially enable full system compromise through privilege escalation attacks. An attacker with local userspace access can leverage this buffer overflow to execute arbitrary code within kernel space, effectively gaining root privileges and complete control over the affected device. The vulnerability affects all Android releases from the Code Aurora Forum (CAF) that utilize the Linux kernel, indicating a widespread impact across multiple device manufacturers and hardware platforms. This includes smartphones, tablets, and other mobile devices that rely on HDMI output capabilities and the associated kernel subsystems. The attack surface is particularly concerning given that HDMI EDID management is a common functionality in mobile devices that support external display connections, making this vulnerability exploitable in real-world scenarios where users connect their devices to external displays.
Mitigation strategies for CVE-2017-9722 must address both immediate patching requirements and long-term architectural improvements in kernel memory management. Device manufacturers should prioritize applying kernel patches that implement proper bounds checking for the edid_size parameter, ensuring that all userspace input is validated before being processed in kernel space. The recommended solution involves implementing strict buffer size validation and using kernel-safe memory manipulation functions that prevent buffer overflows. Additionally, system administrators should consider implementing kernel lockdown mechanisms and restricting access to the hdmi_tx_sysfs_wta_edid interface to trusted applications only. This vulnerability demonstrates the importance of following secure coding practices as outlined in the CERT Secure Coding Standards, particularly regarding input validation and memory safety. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting kernel-level exploits that leverage memory corruption flaws to gain elevated system privileges, making it a critical concern for mobile security postures and device hardening initiatives.