# CVE-2026-33662: OP-TEE OS integer underflow in RSASSA-PKCS1-v1_5 encoding

Source: https://junglewise.ai/threats/cve-2026-33662-op-tee-os-integer-underflow-in-rsassa-pkcs1-v1-5-encoding  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-24. Updated: 2026-06-05  
License: CC BY 4.0 with a link back

CVE-2026-33662 · Severity: high · CVSS 7.5 · Published 2026-04-24

OP-TEE is a secure operating system used on Arm-based devices to protect sensitive data and cryptographic operations. A flaw in how it handles certain digital signature tasks allows an attacker to trigger a system crash by providing a specially crafted cryptographic key. This results in a denial-of-service, potentially disrupting secure device operations or causing the entire system to reboot.

## Quick answers

**Is CVE-2026-33662 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-33662 being exploited in the wild.

**How severe is CVE-2026-33662?** High severity, with a CVSS score of 7.5, published 24 April 2026.

**Which products and versions are affected?** TrustedFirmware OP-TEE OS 3.8.0 to 4.10.0.

**Is there a fix for CVE-2026-33662?** A patch was published on 2026-04-24: Fix published in version 4.11.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-33662 attacked?** It is attacked over the network, in device firmware.

**Am I affected by CVE-2026-33662?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An integer underflow vulnerability exists in the emsa_pkcs1_v1_5_encode() function within core/drivers/crypto/crypto_api/acipher/rsassa.c. The vulnerability occurs when calculating the padding size (PS size) for RSASSA-PKCS1-v1_5 encoding; specifically, subtracting the digest and metadata sizes from a small RSA modulus results in a negative value stored in an unsigned integer. This underflowed value is subsequently passed to memset(), causing a massive heap overwrite with 0xFF bytes until the Trusted Execution Environment (TEE) crashes. The issue specifically affects platforms with RSA acceleration enabled, such as those using NXP CAAM, HiSilicon ACC_V3, or Versal crypto drivers. A fix is available in OP-TEE version 4.11.0.

## Affected products

- TrustedFirmware OP-TEE OS 3.8.0 to 4.10.0

## Timeline

- 2025-12-24: other: Report received by vendor
- 2026-01-07: other: Confirmed as security issue
- 2026-04-24: patched: Fix published in version 4.11.0
- 2026-04-24: advisory: Public disclosure

## References

- [https://github.com/OP-TEE/optee_os/security/advisories/GHSA-4cf8-v5g3-73gr](https://github.com/OP-TEE/optee_os/security/advisories/GHSA-4cf8-v5g3-73gr)