EUVD-2026-21506Published

Step CA affected by an index out of bounds panic in TPM attestation EKU validation

Collected exploitation and prediction evidence

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2026-40097

Published

Step CA is an online certificate authority for secure, automated certificate management for DevOps. From 0.24.0 to before 0.30.0-rc3, an attacker can trigger an index out-of-bounds panic in Step CA by sending a crafted attestation key (AK) certificate with an empty Extended Key Usage (EKU) extension during TPM device attestation. When processing a device-attest-01 ACME challenge using TPM attestation, Step CA validates that the AK certificate contains the tcg-kp-AIKCertificate Extended Key Usage OID. During this validation, the EKU extension value is decoded from its ASN.1 representation and the first element is checked. A crafted certificate could include an EKU extension that decodes to an empty sequence, causing the code to panic when accessing the first element of the empty slice. This vulnerability is only reachable when a device-attest-01 ACME challenge with TPM attestation is configured. Deployments not using TPM device attestation are not affected. This vulnerability is fixed in 0.30.0-rc3.

Source published: 10 Apr 2026 16:34:53 UTC
Source modified: 10 Apr 2026 18:30:15 UTC
Observed here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

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

euvd · EUVD-2026-21506

Published

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Apr 10, 2026, 4:34:53 PM

dateUpdated: Apr 10, 2026, 6:30:15 PM

Source published: Apr 10, 2026, 4:34:53 PM (timezone not stated)
Source modified: Apr 10, 2026, 6:30:15 PM (timezone not stated)
Observed here: 1 Nov 2026 06:15:12 UTC
Source terms: ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

nvd · CVE-2026-40097

Published

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Analyzed

Weakness classifications: CWE-129

Original publisher date fields

published: 2026-04-10T17:17:12.823

lastModified: 2026-10-26T22:10:00.163

3 source CPE criteria · context only

cpe:2.3:a:smallstep:step-ca:*:*:*:*:*:go:*:*
cpe:2.3:a:smallstep:step-ca:0.30.0:rc1:*:*:*:go:*:*
cpe:2.3:a:smallstep:step-ca:0.30.0:rc2:*:*:*:go:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published: 10 Apr 2026 17:17:12 UTC
Source modified: 26 Oct 2026 22:10:00 UTC
Observed here: 27 Oct 2026 10:09:56 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

osv · GHSA-9qq8-cgcv-qmc9

Published

# Summary An attacker can trigger an index out-of-bounds panic in Step CA by sending a crafted attestation key (AK) certificate with an empty Extended Key Usage (EKU) extension during TPM device attestation. ## Details When processing a device-attest-01 ACME challenge using TPM attestation, Step CA validates that the AK certificate contains the tcg-kp-AIKCertificate Extended Key Usage OID. During this validation, the EKU extension value is decoded from its ASN.1 representation and the first element is checked. A crafted certificate could include an EKU extension that decodes to an empty sequence, causing the code to panic when accessing the first element of the empty slice. This vulnerability is only reachable when a device-attest-01 ACME challenge with TPM attestation is configured. Deployments not using TPM device attestation are not affected. ## Mitigations If you are unable to upgrade to v0.30.0 or newer, the attack can be mitigated by disabling or removing any ACME provisioners that use TPM device attestation (device-attest-01). ## Fix In v0.30.0, a bounds check was added to validateAKCertificateExtendedKeyUsage so that an empty EKU sequence is treated as a validation failure rather than causing a panic. ## Acknowledgements This issue was identified and reported by @1seal (Oleh Konko). ## Embargo List If your organization runs Step CA in production and would like advance, embargoed notification of future security updates, visit https://u.step.sm/disclosure to request inclusion on our embargo list. Stay safe, and thank you for helping us keep the ecosystem secure.

Source published: 10 Apr 2026 20:18:08 UTC
Source modified: 25 Jun 2026 19:56:06 UTC
Observed here: 24 Oct 2026 13:19:41 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Publisher rating · LOW

osv · GO-2026-5297

Published

Step CA affected by an index out of bounds panic in TPM attestation EKU validation in github.com/smallstep/certificates

Source published: 25 Jun 2026 18:43:19 UTC
Source modified: 25 Jun 2026 19:45:30 UTC
Observed here: 24 Oct 2026 13:19:41 UTC
Source terms: OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.