CVE-2021-44733

What it actually does

Use-after-free in tee_shm_get_from_id caused by a race condition during shared memory object freeing in the TEE subsystem, enabling local memory corruption and potential privilege escalation.

Why it matters to the business

Local attackers can achieve full system compromise on unpatched Linux kernels, risking data exposure and service disruption; the issue has been public for years with exploits available but low observed exploitation rates reduce immediate urgency.

How an attack unfolds

An attacker with local access triggers the race condition in tee_shm_get_from_id to free a shared memory object while it is still referenced, then leverages the resulting use-after-free for arbitrary code execution or privilege escalation; listed threat actors reference generic kernel race and overflow techniques.

How to fix it

Apply the upstream fix from commit dfd0743f1d9ea76931510ed150334d571fbab49d or upgrade to a Linux kernel version containing that change; rebuild and reboot affected systems.

How to confirm the fix worked

Verify the running kernel contains commit dfd0743f1d9ea76931510ed150334d571fbab49d via git log or package version checks; test TEE workloads for absence of use-after-free crashes under concurrent access.

Typical attack path

1. Obtain local user access on a vulnerable Linux system
2. Invoke TEE subsystem calls to allocate shared memory objects
3. Race tee_shm_get_from_id to trigger premature free of the object
4. Reuse the dangling reference to corrupt kernel memory structures
5. Escalate privileges or execute arbitrary code in kernel context

How to detect it

Review kernel logs and dmesg for use-after-free warnings or oops traces involving tee_shm; search audit and system logs for unusual TEE subsystem activity around the time of suspected compromise.

• tee_shm_get_from_id
• drivers/tee/tee_shm.c
• use-after-free in TEE shared memory

What your security team should do

• Patch all Linux systems to the fixed commit within standard change windows given low EPSS and no KEV listing
• Monitor for kernel oops or TEE-related crashes as potential indicators
• Restrict local access to TEE-capable devices where feasible