CVE-2026-33662 OP-TEE: RSASSA EMSA- PKCS1-v1_5 underflow in emsa_pkcs1_v1_5_encode()
An integer underflow in OP-TEE's RSA padding calculation allows attackers to crash the Trusted Execution Environment on platforms with RSA acceleration.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-33662?
CVE-2026-33662 is a high-severity vulnerability in OP-TEE optee_os, published on 24 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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. From 3.8.0 to 4.10, in the function emsa_pkcs1_v1_5_encode() in core/drivers/crypto/crypto_api/acipher/rsassa.c, the amount of padding needed, "PS size", is calculated by subtracting the size of the digest and other fields required for the EMA-PKCS1-v1_5 encoding from the size of the modulus of the key. By selecting a small enough modulus, this subtraction can overflow. The padding is added as a string of 0xFF bytes with a call to memset(), and an underflowed integer will cause the memset() call to overwrite until OP-TEE crashes. This only affects platforms registering RSA acceleration.
Weakness: CWE-190
Which versions are affected by CVE-2026-33662?
It affects 1 product.
Products include Trustedfirmware Op-Tee.
How do I fix CVE-2026-33662?
No fix has been published for CVE-2026-33662 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-33662 being exploited?
There is no known exploitation of CVE-2026-33662 in the wild and no public exploit code.
Other vulnerabilities in OP-TEE optee_os
Sources
Also known as DEBIAN-CVE-2026-33662, GHSA-4cf8-v5g3-73gr, UBUNTU-CVE-2026-33662.