CVE-2026-53210: Linux Kernel Information Disclosure Bug

CVE-2026-53210 Overview

CVE-2026-53210 is a memory leak vulnerability in the Linux kernel's Trusted Execution Environment (TEE) subsystem. The flaw resides in the register_shm_helper() function, which manages shared memory registration between user space and trusted applications. When iov_iter_npages() returns 0, the function jumps to the err_ctx_put label without freeing the previously allocated shm structure. Local users can trigger the leak through the TEE_IOC_SHM_REGISTER ioctl by supplying a tee_ioctl_shm_register_data structure with a length field of 0. Repeated invocation can exhaust kernel memory over time.

Critical Impact
Local unprivileged users can trigger a kernel memory leak through a crafted ioctl call, potentially leading to resource exhaustion and degraded system stability.

Affected Products

Linux kernel versions containing the vulnerable register_shm_helper() implementation in drivers/tee/
Systems with the TEE subsystem enabled (commonly ARM TrustZone-based platforms)
Distributions shipping pre-patch stable kernel branches referenced in the upstream commits

Discovery Timeline

2026-06-25 - CVE-2026-53210 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53210

Vulnerability Analysis

The vulnerability exists in the Linux kernel TEE subsystem within register_shm_helper(). This helper allocates a struct tee_shm object representing a shared memory region. The function then calls iov_iter_npages() to determine the number of pages required for the user-supplied buffer. The original control flow assumed iov_iter_npages() would return a positive value. When the caller supplies a zero-length region, the function returns 0 and the code branches to the err_ctx_put cleanup label.

That cleanup path releases the TEE context reference but does not free the already-allocated shm object. Each invocation leaks the structure and its associated bookkeeping memory. Because the trigger is an ordinary ioctl available to processes with access to /dev/tee*, the leak is reachable from unprivileged user space on systems exposing the TEE device node.

Root Cause

The root cause is incorrect error-handling flow [CWE-401: Missing Release of Memory after Effective Lifetime]. The function performs resource allocation before validating the return value of iov_iter_npages(), and the wrong cleanup label is used when that validation fails. The fix redirects the zero-page case to the err_free_shm label, which releases the shm allocation before returning the error.

Attack Vector

An attacker with local access and permission to open the TEE device can issue repeated TEE_IOC_SHM_REGISTER ioctls with struct tee_ioctl_shm_register_data.length set to 0. Each call leaks kernel memory associated with the failed registration. Sustained exploitation can exhaust kernel slab memory and degrade or destabilize the host. The vulnerability does not provide code execution or direct privilege escalation but constitutes a local denial-of-service primitive.

The vulnerability is described in detail in the upstream fix commits. See the Kernel Git Commit 26682f5, Kernel Git Commit 4277759, Kernel Git Commit c10c9c4, and Kernel Git Commit dbf779d for the patch contents.

Detection Methods for CVE-2026-53210

Indicators of Compromise

Steady, unexplained growth in kernel slab allocations associated with tee_shm objects observable in /proc/slabinfo.
Repeated TEE_IOC_SHM_REGISTER ioctls from a single process with length=0 parameters in audit logs.
Gradual reduction in MemAvailable on systems running TEE-enabled kernels without a corresponding workload increase.

Detection Strategies

Enable Linux audit rules on the ioctl syscall against /dev/tee* device nodes and review for high-frequency calls from unexpected processes.
Monitor kernel memory metrics over time and alert on sustained growth in TEE-related slab caches.
Use eBPF tracing on register_shm_helper to capture caller PIDs and argument lengths when the function exits via the error path.

Monitoring Recommendations

Correlate process telemetry with kernel memory pressure events to identify userspace processes driving slab growth.
Track kernel version inventory and flag hosts running pre-patch stable kernels exposing /dev/tee*.
Alert on out-of-memory events on TEE-enabled hardware platforms such as ARM TrustZone devices.

How to Mitigate CVE-2026-53210

Immediate Actions Required

Apply the upstream stable kernel updates containing commits 26682f5, 4277759, c10c9c4, or dbf779d as appropriate for your kernel branch.
Inventory systems exposing /dev/tee* device nodes and restrict access to trusted users and services only.
Reboot affected hosts after patching to ensure the fixed kernel is active.

Patch Information

The fix replaces the erroneous goto err_ctx_put with goto err_free_shm when iov_iter_npages() returns 0, ensuring the shm structure is freed on the error path. Patches are available in the upstream stable trees referenced in Kernel Git Commit 26682f5 and the related commits. Distribution maintainers have backported the change to supported stable branches.

Workarounds

Where the TEE subsystem is not required, unload or disable the tee and associated backend modules (for example optee).
Restrict permissions on /dev/tee* nodes via udev rules to prevent unprivileged access until patching is complete.
Apply mandatory access control policies (SELinux or AppArmor) to limit which processes may issue ioctls against TEE devices.

bash

# Configuration example: restrict TEE device access via udev
# /etc/udev/rules.d/90-tee-restrict.rules
KERNEL=="tee[0-9]*", MODE="0600", OWNER="root", GROUP="root"
KERNEL=="teepriv[0-9]*", MODE="0600", OWNER="root", GROUP="root"

# Reload udev rules
sudo udevadm control --reload-rules
sudo udevadm trigger