# CVE-2026-6458: AES-256-GCM Authentication Tag Does Not Cover First Ciphertext Blocks When AAD Is Empty

> Attackers can modify initial ciphertext blocks without detection due to incorrect GCM tag calculation when AAD is empty in Caliptra firmware.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:A/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **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-834g-h5x6-2hqr

## What is CVE-2026-6458?

CVE-2026-6458 is a medium-severity 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

Missing cryptographic step in Caliptra Core Firmware (aes_256_gcm_update module) results in an incorrect GCM authentication tag. When the streaming AES-256-GCM API is used with empty AAD, the hardware GHASH accumulator state is not saved after the first update call, causing the final tag to exclude the first batch of processed ciphertext. Ciphertext produced by that call may be modified without the tag reflecting the change.

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

Weakness: CWE-325 (Missing Cryptographic Step)

## Which versions are affected by CVE-2026-6458?


## How do I fix CVE-2026-6458?

No fix has been published for CVE-2026-6458 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6458 being exploited?

There is no known exploitation of CVE-2026-6458 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6458 and fix it if it is affected.

What it is: CVE-2026-6458 is a medium-severity 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-2026-6458 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-2026-6458/ (Markdown: https://insights.sbomify.com/CVE-2026-6458/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6458
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6458
- OSV: https://osv.dev/vulnerability/CVE-2026-6458

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-6458/
Summaries are generated and may contain mistakes; the official description above is the record.