OP-TEE is a Trusted Execution Environment (TEE) designed as companion to a non-secure Linux kernel running on Arm; Cortex-A cores using the TrustZone technology. Starting in version 3.20.0 and prior to version 4.11.0, a vulnerability in OP-TEE’s subkey rollback protection allows the use of revoked or older subkey versions because the system fails to propagate versioning data during the Trusted Application (TA) loading process. In "core/crypto/signed_hdr.c", the function "shdr_load_pub_key()" parses subkey headers but does not assign the "subkey_version" to the runtime "shdr_pub_key" structure. As a result, the "key->version" field remains at zero regardless of the version specified in the header. When "ree_fs_ta_open()" in "core/kernel/ree_fs_ta.c" calls "check_update_version()", it passes this zeroed version to the rollback database. Because the database never receives a non-zero version to record, it never advances, effectively bypassing the rollback check and allowing TAs signed with downgraded subkey chains to load successfully. This impacts OP-TEE mainline configurations that utilize subkey-based signing chains for Trusted Application (TA) authentication. Version 4.11.0 contains a patch. No known workarounds are available.