CVE-2026-89898 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
media: cec: extron-da-hd-4k-plus: add sanity check
Add check to prevent overflowing msg.msg[] in case the incoming data
is malformed.
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Analysis
by VulDB Data Team • 09/16/2026
The Common Exploration Format (CEC) subsystem within the Linux kernel provides support for consumer electronics control protocols, allowing devices connected via HDMI to communicate and interact with one another. A specific driver implementation for the Extron DA-HD-4K Plus device contained a critical input validation flaw that could lead to memory corruption. The vulnerability arises from insufficient boundary checking when processing incoming CEC messages. Specifically, the code failed to verify whether the length of an incoming message exceeded the allocated size of the msg.msg array before copying or accessing data into it. This lack of sanity check creates a classic buffer overflow condition where malformed or maliciously crafted input can write beyond the intended memory boundaries.
From a technical perspective, this flaw represents a failure in proper input validation and boundary checking, which are fundamental principles of secure coding practices. When an attacker sends a CEC message with a length field indicating more data than fits within the fixed-size buffer, the kernel will proceed to copy that excess data into adjacent memory locations. This can overwrite critical kernel structures such as function pointers, return addresses, or other control data stored on the stack or in heap metadata depending on how the driver manages its internal state. The absence of a length check means the system trusts user-supplied input without verification, violating the principle of least privilege and robust error handling expected in operating system kernels.
The operational impact of this vulnerability is severe due to its location within the kernel space. Successful exploitation could allow an attacker with physical access to the HDMI port or potentially through network-adjacent CEC implementations to achieve arbitrary code execution with root privileges. This compromises the integrity, availability, and confidentiality of the entire system running the Linux kernel. In embedded systems or media servers where such drivers are commonly deployed, this could lead to complete system takeover, denial of service through kernel panic caused by memory corruption, or lateral movement within a local network if the compromised device serves as an entry point for further attacks.
This vulnerability aligns with CWE-120 Buffer Copy without Checking Size of Input and CWE-20 Improper Input Validation according to the Common Weakness Enumeration standard. In terms of attack tactics, it relates to ATT&CK technique T1059 Command and Scripting Interpreter if exploitation leads to code execution, or more broadly to initial access vectors involving physical interface manipulation such as HDMI-based attacks documented in various hardware hacking communities. The fix involves adding a strict sanity check that validates the message length against the maximum allowed size of the msg.msg array before any data transfer occurs. If the incoming data exceeds this limit, the driver should reject the message and log an error rather than attempting to process it.
Mitigation strategies for organizations relying on affected Linux kernels include applying vendor-provided security patches as soon as they become available. For systems where immediate patching is not feasible, physical isolation of HDMI ports from untrusted devices can reduce exposure risk since CEC attacks typically require direct connection to the display or media device interface. Additionally, enabling kernel hardening features such as stack protector and KASLR may mitigate some exploitation attempts by making it harder for attackers to reliably predict memory layouts and execute arbitrary code even if a buffer overflow occurs. Regular auditing of driver code for similar input validation gaps is also recommended to prevent recurrence of this class of vulnerabilities across the media subsystem.