CVE-2026-40097: CWE-129: Improper Validation of Array Index in smallstep certificates
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.
AI Analysis
Technical Summary
Step CA versions >= 0.24.0 and < 0.30.0-rc3 contain a vulnerability (CWE-129) where the EKU extension in an attestation key certificate is decoded and the first element is accessed without verifying the sequence is non-empty. If the EKU extension is an empty sequence, this causes an index out-of-bounds panic during TPM device attestation in device-attest-01 ACME challenges. This vulnerability is not reachable unless TPM device attestation is configured. The issue is fixed in version 0.30.0-rc3.
Potential Impact
The vulnerability causes a denial of service via an index out-of-bounds panic in Step CA when processing a crafted attestation key certificate during TPM device attestation. There is no confidentiality, integrity, or authentication impact reported. Exploitation requires network access and the use of TPM device attestation. The CVSS score is 3.7 (low severity).
Mitigation Recommendations
Upgrade Step CA to version 0.30.0-rc3 or later where this vulnerability is fixed. Deployments not using TPM device attestation are not affected. No other mitigations are indicated.
CVE-2026-40097: CWE-129: Improper Validation of Array Index in smallstep certificates
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Step CA versions >= 0.24.0 and < 0.30.0-rc3 contain a vulnerability (CWE-129) where the EKU extension in an attestation key certificate is decoded and the first element is accessed without verifying the sequence is non-empty. If the EKU extension is an empty sequence, this causes an index out-of-bounds panic during TPM device attestation in device-attest-01 ACME challenges. This vulnerability is not reachable unless TPM device attestation is configured. The issue is fixed in version 0.30.0-rc3.
Potential Impact
The vulnerability causes a denial of service via an index out-of-bounds panic in Step CA when processing a crafted attestation key certificate during TPM device attestation. There is no confidentiality, integrity, or authentication impact reported. Exploitation requires network access and the use of TPM device attestation. The CVSS score is 3.7 (low severity).
Mitigation Recommendations
Upgrade Step CA to version 0.30.0-rc3 or later where this vulnerability is fixed. Deployments not using TPM device attestation are not affected. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-09T01:41:38.536Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69d9d9721cc7ad14da3f8637
Added to database: 4/11/2026, 5:17:38 AM
Last enriched: 4/11/2026, 5:18:17 AM
Last updated: 4/11/2026, 3:22:06 PM
Views: 8
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