- Exploited
- No known exploitation
- Fix
- Fixed in 0.39.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.39.0.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 16/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
AWS-LC, the cryptographic library used via the aws-lc-sys package, can be tricked by certificates with wildcard or raw Unicode Common Name values, which bypass X.509 name constraints checks while still being accepted for hostname verification. Applications are not affected if they disable CN fallback with X509_CHECK_FLAG_NEVER_CHECK_SUBJECT or only see certificates that use dNSName SANs, and the fix is to upgrade aws-lc-sys.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
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.
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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach16/20aws-lc-sys: 9.1M downloads a week
- Severity?/10Unknown. No CVSS score or vendor rating
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
- Would score about 38 if advisories confirm default setups are exposed
Impact
- Widely used
aws-lc-sys has 9.1m weekly downloads.Source: crates.io
What to do
Upgrade to a fixed version: 0.39.0.
Timeline
- Advisory published235 days
- Record last updated
Affected versions
- aws-lc-syscrates.io
From 0.32.0 · fixed in 0.39.0
Fixed in 0.39.0 (released Mar 19, 2026, the day of disclosure).
The latest release, 0.47.0, is not affected.
Evidence 2
- Advisory
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about RUSTSEC-2026-0044
Is RUSTSEC-2026-0044 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by RUSTSEC-2026-0044?
aws-lc-sys (crates.io): from 0.32.0 before 0.39.0.Source: cve.now feed data
How do I fix RUSTSEC-2026-0044?
Upgrade to a fixed version: 0.39.0.Source: cve.now feed data