How severe is CVE-2026-40097?

CVE-2026-40097 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2026-40097 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40097?

CVE-2026-40097 primarily affects Smallstep Step-ca. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-40097?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40097 have an EU (EUVD) identifier?

Yes. CVE-2026-40097 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21506.

When was CVE-2026-40097 published?

CVE-2026-40097 was published on 2026-04-10 and last updated on 2026-06-17.

CVE-2026-40097

CVE-2026-40097 is a low-severity vulnerability in Smallstep Step-ca with a CVSS 3.x base score of 3.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-129.

Key facts

Severity: Low (CVSS 3.x base score 3.7)
EPSS exploit prediction: 0% (8th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-21506
Weakness: CWE-129
Affected product: Smallstep Step-ca
Published: 2026-04-10
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-40097?: 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.
How severe is CVE-2026-40097?: CVE-2026-40097 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-40097 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40097?: CVE-2026-40097 primarily affects Smallstep Step-ca. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-40097?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40097 have an EU (EUVD) identifier?: Yes. CVE-2026-40097 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21506.
When was CVE-2026-40097 published?: CVE-2026-40097 was published on 2026-04-10 and last updated on 2026-06-17.

References

Affected products (3)

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:*:*

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