CVE-2020-36766 in Linux
Summary
by MITRE • 09/18/2023
An issue was discovered in the Linux kernel before 5.8.6. drivers/media/cec/core/cec-api.c leaks one byte of kernel memory on specific hardware to unprivileged users, because of directly assigning log_addrs with a hole in the struct.
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Analysis
by VulDB Data Team • 10/12/2023
The vulnerability identified as CVE-2020-36766 represents a critical information disclosure flaw within the Linux kernel's CEC (Consumer Electronics Control) subsystem. This vulnerability affects versions prior to 5.8.6 and specifically targets the cec-api.c file located in the drivers/media/cec/core/ directory. The issue manifests as a memory disclosure attack that allows unprivileged users to access one byte of kernel memory, potentially exposing sensitive information that should remain confidential within the kernel space. The flaw occurs due to improper handling of memory allocation within the CEC subsystem's address management structure.
The technical root cause of this vulnerability stems from a direct assignment operation involving the log_addrs field within a structure that contains a memory hole or padding gap. This memory hole creates an opportunity for information leakage when the kernel assigns values to the log_addrs field without proper sanitization. The structure's layout includes unused memory regions that are not cleared before assignment, allowing residual kernel data to persist in memory locations that are subsequently exposed to userspace. This type of vulnerability falls under the CWE-248 category of Uncaught Exception and represents a classic case of improper initialization leading to information exposure.
The operational impact of this vulnerability is significant for systems running affected Linux kernel versions, particularly those with CEC hardware support. An unprivileged local user can exploit this flaw to extract one byte of kernel memory, which may contain sensitive data such as cryptographic keys, passwords, session tokens, or other confidential information. The exposure of kernel memory can potentially lead to further exploitation opportunities, including privilege escalation attacks or the discovery of additional vulnerabilities within the kernel's memory space. This vulnerability directly violates the principle of least privilege and compromises the kernel's memory protection mechanisms that are essential for maintaining system security boundaries.
Security practitioners should prioritize patching affected systems with kernel versions 5.8.6 or later, as this release contains the necessary fixes for the memory disclosure issue. Organizations should also implement monitoring for suspicious memory access patterns and consider restricting access to CEC hardware when not required for system operation. The vulnerability demonstrates the importance of proper memory initialization and the potential risks associated with direct memory assignments in kernel code. This issue aligns with ATT&CK technique T1059.001 for command and scripting interpreter, as exploitation may involve crafting specific CEC commands to trigger the memory disclosure, and T1068 for exploit for privilege escalation through information disclosure. System administrators should also consider implementing kernel lockdown modes and other security hardening measures to mitigate the risk of such information disclosure vulnerabilities.