The vulnerability is a Bleichenbacher‑style padding oracle discovered in the Hisilicon HPRE crypto driver of OP‑TEE’s Trusted Execution Environment. The driver’s RSA PKCS#1 v1.5 decryption routine uses a non‑constant‑time memcmp() to verify a label hash and contains multiple distinguishable error paths that an attacker can use to determine whether a decrypted plaintext meets the padding requirements. By repeatedly querying the driver with carefully crafted ciphertexts, an attacker can recover the RSA‑encrypted plaintext, thereby compromising the confidentiality of data processed within the trusted domain. The likely attack vector is an entity that can supply ciphertext to the HPRE RSA driver, such as code running inside or that can feed data to the OP‑TEE subsystem. Based on the description, it is inferred that the attacker need not have privileged access; the side‑channel can be exploited via repeated decryption requests sent to the driver from within the trusted domain.

The flaw affects OP‑TEE versions 4.5.0 through 4.10.x on devices that enable the Hisilicon HPRE crypto driver. The affected code resides in the OP‑TEE open‑source OS, typically run on ARM Cortex‑A cores with TrustZone support. A patch was introduced in version 4.11.0 to eliminate the timing side channel and consolidate error handling, and a workaround is to disable the driver by setting CFG_HISILICON_ACC_V3=n.

The CVSS score is 2.5, indicating low overall severity. The vulnerability is not listed in CISA KEV and the EPSS score is < 1 %, suggesting limited exploitation data. Nevertheless, a successful padding oracle attack could allow an attacker to decrypt sensitive RSA‑encrypted data. The attack surface is constrained to systems that load the Hisilicon HPRE RSA driver, but the impact of decrypting confidential information is significant. The likely attack vector is gaining the ability to issue decryption requests to the driver; based on the description, it is inferred that this may be achievable from code executing within the TEE or via manipulation of data supplied to the trusted environment.