# GHSA-394x-vwmw-crm3: AWS-LC X.509 Name Constraints Bypass via Wildcard/Unicode CN

> A logic error in AWS-LC allows certificates with wildcard or Unicode Common Names to bypass name constraints, enabling potential man-in-the-middle attacks.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Mar 2026
- **Also known as:** RUSTSEC-2026-0044

## What is GHSA-394x-vwmw-crm3?

GHSA-394x-vwmw-crm3 is a vulnerability in aws-lc-sys, published on 19 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

### Summary

AWS-LC is an open-source, general-purpose cryptographic library.

### Impact

A logic error in CN (Common Name) validation allows certificates with wildcard or raw UTF-8 Unicode CN values to bypass name constraints enforcement. The `cn2dnsid` function does not recognize these CN patterns as valid DNS identifiers, causing `NAME_CONSTRAINTS_check_CN` to skip validation. However, `X509_check_host` accepts these CN values when no dNSName SAN is present, allowing certificates to bypass name constraints while still being used for hostname verification.

Customers of AWS services do not need to take action. Applications using aws-lc-sys should upgrade to the most recent release of aws-lc-sys.

### Impacted versions:

* aws-lc-sys >= v0.32.0, < v0.39.0

### Patches

The patch is included in aws-lc-sys v0.39.0.

### Workarounds

Applications that set `X509_CHECK_FLAG_NEVER_CHECK_SUBJECT` to disable CN fallback are not affected. Applications that only encounter certificates with dNSName SANs (standard for public WebPKI) are also not affected.

Otherwise, there is no workaround and applications using aws-lc-sys should upgrade to the most recent releases of aws-lc-sys.

### References

If you have any questions or comments about this advisory, we ask that you contact AWS Security via our [vulnerability reporting page](https://aws.amazon.com/security/vulnerability-reporting/) or directly via email to [aws-security@amazon.com](mailto:aws-security@amazon.com). Please do not create a public GitHub issue.

### Credits

Oleh Konko from 1seal (https://1seal.org/)

## Which versions are affected by GHSA-394x-vwmw-crm3?

3 open source packages ship an affected version, including aws-lc-sys.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `aws-lc-sys` | crates.io | From 0.32.0 | 0.39.0 |
| `aws-lc-sys` | crates.io | From 0.32.0 | 0.39.0 |
| `aws-lc-sys` | crates.io | From 0.32.0 | 0.39.0 |

## How do I fix GHSA-394x-vwmw-crm3?

Upgrade aws-lc-sys to 0.39.0 or later.

## Is GHSA-394x-vwmw-crm3 being exploited?

There is no known exploitation of GHSA-394x-vwmw-crm3 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-394x-vwmw-crm3 and fix it if it is affected.

What it is: GHSA-394x-vwmw-crm3 is a vulnerability in aws-lc-sys, published on 19 Mar 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 GHSA-394x-vwmw-crm3 in the wild and no public exploit code.

Affected packages and fixed versions:
- aws-lc-sys (crates.io): affected from 0.32.0; fixed in 0.39.0
- aws-lc-sys (crates.io): affected from 0.32.0; fixed in 0.39.0
- aws-lc-sys (crates.io): affected from 0.32.0; fixed in 0.39.0

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/GHSA-394x-vwmw-crm3/ (Markdown: https://insights.sbomify.com/GHSA-394x-vwmw-crm3/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-394x-vwmw-crm3

---
From sbomify Insights: https://insights.sbomify.com/GHSA-394x-vwmw-crm3/
Summaries are generated and may contain mistakes; the official description above is the record.