OP-TEE OS through 4.10.0, fixed in commit 8794043, contains a use-after-free vulnerability in the Trusted Application loader that allows attackers with the ability to load a signed Trusted Application to corrupt secure-world kernel memory by setting the TA_FLAG_CONCURRENT flag in a user TA signed header. Attackers can cause two concurrent sessions to operate on the same shared context without locking, corrupting the uctx->vm_info.regions list during memref parameter mapping and unmapping to free vm_region nodes still in use, resulting in a use-after-free in S-EL1 secure-world kernel memory.