# CVE-2026-5818: MCU Firmware Update Authentication Bypass on Caliptra Core

> Attackers can bypass MCU firmware verification during hitless updates due to incorrect return value checks in Caliptra Core Runtime Firmware.

- **Severity:** High 7.2 (`CVSS:4.0/AV:A/AC:L/AT:P/PR:H/UI:N/VC:N/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Jun 2026
- **Updated:** 24 Jun 2026
- **Also known as:** GHSA-456r-gcjr-6rxq

## What is CVE-2026-5818?

CVE-2026-5818 is a high-severity authentication bypass vulnerability in Caliptra Core Runtime Firmware, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Incorrect check of function return value in Caliptra Core Runtime Firmware (ActivateFirmwareCmd::activate_fw modules) allows bypass of Caliptra Core's verification of the MCU FW during a hitless update.

This issue affects Core Runtime Firmware: from 2.0.0 through 2.0.1, 2.1.0.

Weakness: CWE-253 (Incorrect Check of Function Return Value)

## Which versions are affected by CVE-2026-5818?


## How do I fix CVE-2026-5818?

No fix has been published for CVE-2026-5818 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-5818 being exploited?

There is no known exploitation of CVE-2026-5818 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-5818 and fix it if it is affected.

What it is: CVE-2026-5818 is a high-severity authentication bypass vulnerability in Caliptra Core Runtime Firmware, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-5818 in the wild and no public exploit code.

Affected product: Caliptra Core Runtime Firmware. 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-2026-5818/ (Markdown: https://insights.sbomify.com/CVE-2026-5818/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-5818
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5818
- OSV: https://osv.dev/vulnerability/CVE-2026-5818

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-5818/
Summaries are generated and may contain mistakes; the official description above is the record.