An integer underflow in the padding calculation of the RSASSA EMSA-1_5 encoding routine causes a negative padding size, which is passed to memset and results in an out‑of‑bounds memory overwrite. The exploit triggers a crash of the OP‑TEE Trusted Execution Environment, leading to a denial of service. The vulnerability is a classic integer overflow condition (CWE‑190).

The flaw is present in OP‑TEE versions 3.8.0 through 4.10 on Arm Cortex‑A platforms that register RSA acceleration. It does not affect other OP‑TEE releases or platforms that do not enable RSA acceleration.

The CVSS score of 7.5 indicates high severity, yet the EPSS score of < 1% signals a very low likelihood of exploitation. The vulnerability is not listed in the CISA KEV catalog. Because the flaw requires triggering RSA operations with a small modulus on a system that supports RSA acceleration, the attack vector is inferred to be local or via an application that performs such operations. If exploited, an attacker can force OP‑TEE to crash but cannot directly compromise data or obtain read/write access to the secure world. The overall risk is moderate to high for environments that rely on OP‑TEE for cryptographic services, but the exploitation probability remains low.