CVE-2026-4428Public exploitNetwork attack vector

Certificate-validation bypass via skipped CRL scope matching

Published Mar 19, 2026 · Updated Mar 19, 2026

Certificate validation bypass in AWS-LC before 1.71.0 and AWS-LC-FIPS before 3.3.0 allows remote attackers to have revoked certificates accepted. In crypto/x509/x509_vfy.c, crl_crldp_check() combines disqualifying CRLissuer and reasons fields with &&, returns instead of continuing, and runs idp_check_dp in the wrong branch, so clean distribution points never match IDP-scoped CRLs. Exposure requires X509_V_FLAG_CRL_CHECK and partitioned CRLs with IDP extensions; complete CRLs and disabled CRL checking are unaffected.

CVSS severity9.1
Critical
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Certificate validation bypass in AWS-LC before 1.71.0 and AWS-LC-FIPS before 3.3.0 allows remote attackers to have revoked certificates accepted. In crypto/x509/x509_vfy.c, crl_crldp_check() combines disqualifying CRLissuer and reasons fields with &&, returns instead of continuing, and runs idp_check_dp in the wrong branch, so clean distribution points never match IDP-scoped CRLs. Exposure requires X509_V_FLAG_CRL_CHECK and partitioned CRLs with IDP extensions; complete CRLs and disabled CRL checking are unaffected.

The record

CVE
CVE-2026-4428
Published
Mar 19, 2026
Updated
Mar 19, 2026
Vendor
Amazon Web Services
Product
AWS-LC
Classifications
CWE-299
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.24.0 <1.71.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Amazon Web Services · AWS-LCversion=1.24.0 <1.71.0
Amazon Web Services · AWS-LC-FIPSversion=3.0.0 <3.3.0

Published CVSS scores

7.4Amazon Web Services GitHub Security AdvisoryCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
9.1Amazon Web ServicesCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-299Improper Check for Certificate Revocation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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