# RUSTSEC-2026-0209: AES-GCM did not enforce limits on AAD length

> The library fails to enforce AAD length limits, allowing attackers to degrade authentication security in AES-GCM operations.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Jun 2026

## What is RUSTSEC-2026-0209?

RUSTSEC-2026-0209 is a vulnerability in libcrux-aesgcm, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

NIST Special Publication 800-38D specifies that the bit length of the
AAD shall not exceed `2^64 - 1` bits. The implementation of AES-GCM in
`libcrux-aesgcm` neither enforced this limit for encryption nor for
decryption.

## Impact
Use of AES-GCM with AAD of length exceeding the prescribed maximum
length degrades the authentication security of the GCM tag.

## Mitigation
Starting from version `0.0.9` (published as `libcrux-aes@v0.0.9`),
limits on the length of the AAD input are enforced, so overlong AAD
inputs result in an error on encryption and decryption.

## Which versions are affected by RUSTSEC-2026-0209?

1 open source package ship an affected version, including libcrux-aesgcm.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `libcrux-aesgcm` | crates.io | From 0.0.0-0 | None |

## How do I fix RUSTSEC-2026-0209?

No fix has been published for RUSTSEC-2026-0209 yet. Limit exposure of the affected software until one is available.

## Is RUSTSEC-2026-0209 being exploited?

There is no known exploitation of RUSTSEC-2026-0209 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0209 and fix it if it is affected.

What it is: RUSTSEC-2026-0209 is a vulnerability in libcrux-aesgcm, published on 9 Jun 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 RUSTSEC-2026-0209 in the wild and no public exploit code.

Affected packages and fixed versions:
- libcrux-aesgcm (crates.io): affected from 0.0.0-0; no fix listed

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/RUSTSEC-2026-0209/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0209/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0209

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0209/
Summaries are generated and may contain mistakes; the official description above is the record.