CVE-2025-40031 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
tee: fix register_shm_helper()
In register_shm_helper(), fix incorrect error handling for a call to iov_iter_extract_pages(). A case is missing for when iov_iter_extract_pages() only got some pages and return a number larger than 0, but not the requested amount.
This fixes a possible NULL pointer dereference following a bad input from ioctl(TEE_IOC_SHM_REGISTER) where parts of the buffer isn't mapped.
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Analysis
by VulDB Data Team • 05/19/2026
The vulnerability CVE-2025-40031 represents a critical flaw in the Linux kernel's Trusted Execution Environment (TEE) subsystem that specifically affects the tee driver's handling of shared memory registration operations. This issue resides within the register_shm_helper() function which processes ioctl requests for TEE_IOC_SHM_REGISTER, a mechanism that allows user-space applications to register shared memory buffers with the TEE subsystem for secure communication between normal world and trusted world components. The vulnerability stems from inadequate error handling logic when processing memory page extraction operations, creating a potential pathway for system instability and security bypasses.
The technical flaw manifests when the iov_iter_extract_pages() function is invoked during shared memory registration, returning a positive value indicating that some pages were successfully extracted but not the complete requested amount. The current implementation fails to properly handle this intermediate state, missing a crucial code path that should account for partial page extraction scenarios. This omission results in the system proceeding with incomplete memory mapping operations, ultimately leading to a NULL pointer dereference when attempting to access unmapped memory regions. The vulnerability specifically impacts the TEE_IOC_SHM_REGISTER ioctl command where malformed input data causes the kernel to process only partial memory mappings, creating a dangerous state where subsequent memory operations attempt to access invalid pointers.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling privilege escalation and denial of service conditions within systems utilizing TEE subsystems. When exploited, this flaw can cause kernel panics and system instability, particularly affecting devices that rely on secure enclaves such as smartphones, IoT devices, and embedded systems implementing hardware security modules. The vulnerability affects systems running Linux kernels that include the specific TEE driver implementation, making it relevant to a broad range of devices including those using ARM TrustZone technology, Intel SGX, or other TEE implementations that depend on the kernel's shared memory management functions. The issue is particularly concerning in environments where TEE subsystems are used for critical security functions such as secure key storage, cryptographic operations, or protected media decoding.
Mitigation strategies should focus on applying the kernel patch that properly handles the intermediate return values from iov_iter_extract_pages() by implementing comprehensive error checking for partial page extraction scenarios. System administrators should prioritize updating to kernel versions containing the fix, particularly for devices running embedded systems or mobile platforms that heavily utilize TEE functionality. Additional protective measures include implementing strict input validation for TEE ioctl operations and monitoring for unusual patterns in shared memory registration requests that might indicate exploitation attempts. Organizations should also consider implementing runtime protections such as kernel address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts. This vulnerability aligns with CWE-476 which addresses NULL pointer dereferences, and potentially maps to ATT&CK techniques involving privilege escalation through kernel vulnerabilities and system instability exploitation.