# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Apr 2026
- **Updated:** 24 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-33662, GHSA-4cf8-v5g3-73gr, UBUNTU-CVE-2026-33662

## 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 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-33662?

It affects 1 product.


Products: 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

- [CVE-2019-1010292](https://insights.sbomify.com/CVE-2019-1010292/): Memory corruption in OP-TEE (critical 9.8)
- [CVE-2019-1010293](https://insights.sbomify.com/CVE-2019-1010293/): Memory corruption in OP-TEE (critical 9.8)
- [CVE-2019-1010295](https://insights.sbomify.com/CVE-2019-1010295/): Linaro/OP-TEE OP-TEE 3.3.0 and earlier is affected by: Buffer Overflow. (critical 9.8)
- [CVE-2019-1010296](https://insights.sbomify.com/CVE-2019-1010296/): Memory corruption in OP-TEE (critical 9.8)
- [CVE-2019-1010297](https://insights.sbomify.com/CVE-2019-1010297/): Memory corruption in OP-TEE (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33662 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-33662 in the wild and no public exploit code.

Affected product: OP-TEE optee_os. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-33662/ (Markdown: https://insights.sbomify.com/CVE-2026-33662/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33662
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33662
- OSV: https://osv.dev/vulnerability/CVE-2026-33662

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-33662/
Summaries are generated and may contain mistakes; the official description above is the record.