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

GHSA-394x-vwmw-crm3 is a security vulnerability in aws-lc-sys. A fix is available for aws-lc-sys — see the affected versions and patch details below.

Also known asRUSTSEC-2026-0044
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Sep 10, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected
🦀aws-lc-sys

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

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/)

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.ioaws-lc-sys≥ 0.32.0&&< 0.39.00.39.0cargo update -p aws-lc-sys --precise 0.39.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aws-lc-sys, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update aws-lc-sys to 0.39.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-394x-vwmw-crm3 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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
O3 Security · Impact-Aware SCA

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