CVE-2026-40097Network attack vector

Unauthenticated service crash via empty EKU sequence

Published Apr 10, 2026 · Updated Apr 10, 2026

Improper array-index validation in Smallstep step-ca 0.24.0 through 0.30.0-rc2 allows remote attackers to crash the CA during TPM attestation. The validateAKCertificateExtendedKeyUsage function ASN.1-decodes the AK certificate's EKU extension and reads ekus[0] without first checking that the decoded slice contains an element. Reachability requires a device-attest-01 ACME challenge configured for TPM attestation; affected requests panic the CA process and interrupt certificate services.

CVSS severity3.7
Low
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper array-index validation in Smallstep step-ca 0.24.0 through 0.30.0-rc2 allows remote attackers to crash the CA during TPM attestation. The validateAKCertificateExtendedKeyUsage function ASN.1-decodes the AK certificate's EKU extension and reads ekus[0] without first checking that the decoded slice contains an element. Reachability requires a device-attest-01 ACME challenge configured for TPM attestation; affected requests panic the CA process and interrupt certificate services.

The record

CVE
CVE-2026-40097
Published
Apr 10, 2026
Updated
Apr 10, 2026
Vendor
Smallstep
Product
step-ca
Classifications
CWE-129, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 10, 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=>= 0.24.0, < 0.30.0-rc3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Smallstep · step-caversion=>= 0.24.0, < 0.30.0-rc3

Published CVSS scores

3.7GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-129Improper Validation of Array Index
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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