AWS-LC X.509 Name Constraints Bypass via Wildcard/Unicode CN

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

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 NAMECONSTRAINTScheckCN to skip validation. However, X509checkhost 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 X509CHECKFLAGNEVERCHECKSUBJECT to disable CN fallback are not affected. Applications that only encounter certificates with dNSName SANs (standard for public WebPKI) are also…

Published by the source

20 Mar 2026, 20:34 UTC

Last modified by the source

20 Mar 2026, 20:35 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-394x-vwmw-crm3

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# Patch Next advisory brief: GHSA-394x-vwmw-crm3

Advisory: AWS-LC X.509 Name Constraints Bypass via Wildcard/Unicode CN
IDs: GHSA-394x-vwmw-crm3
Record: https://patchnext.com/advisories/ghsa-394x-vwmw-crm3 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: aws-lc-sys 0.39.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io aws-lc-sys: affected >= 0.32.0, < 0.39.0; fixed in 0.39.0

## Suggested inspection (read-only)
- crates.io aws-lc-sys: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on aws-lc-sys.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-394x-vwmw-crm3 (GitHub-reviewed advisory GHSA-394x-vwmw-crm3 lists affected ranges: crates.io aws-lc-sys >=0.32.0 <0.39.0)

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