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

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

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

Q: 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.

Q: How do I fix GHSA-394x-vwmw-crm3?

Upgrade aws-lc-sys to 0.39.0 or later.

Not scored Published 19 Mar 2026

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.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

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 or directly via email to [email protected]. 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?