CVE-2026-33662: OP-TEE RSA Padding Underflow Leads to Crash

The National Vulnerability Database has disclosed CVE-2026-33662, a high-severity vulnerability (CVSS 7.5) affecting OP-TEE, a Trusted Execution Environment (TEE) for Arm Cortex-A cores utilizing TrustZone technology. This flaw, present in versions 3.8.0 to 4.10, resides within the emsa_pkcs1_v1_5_encode() function in core/drivers/crypto/crypto_api/acipher/rsassa.c.

The vulnerability stems from an integer underflow when calculating padding size for RSA PKCS1 v1.5 encoding. Specifically, if a sufficiently small modulus is chosen, the subtraction to determine “PS size” can underflow, leading to an incorrect, larger-than-expected value. This underflowed integer is then used in a memset() call to add padding, causing an out-of-bounds write that ultimately crashes the OP-TEE system.

Crucially, this vulnerability only impacts platforms that have registered RSA acceleration. For defenders, this means any embedded or IoT device leveraging OP-TEE with RSA acceleration is potentially at risk. An attacker could trigger a denial-of-service condition, disrupting critical TEE operations and potentially impacting the integrity or availability of the secure environment. The attacker’s calculus here is straightforward: exploit an integer underflow to induce a crash, achieving a denial of service without requiring complex memory corruption techniques.