smallstep certificates up to 0.30.0-rc2 array index

Summaryinfo

A vulnerability was found in smallstep certificates up to 0.30.0-rc2. It has been declared as problematic. Affected is an unknown function. Such manipulation leads to array index. This vulnerability is traded as CVE-2026-40097. The attack may be launched remotely. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in smallstep certificates up to 0.30.0-rc2. It has been rated as problematic. Affected by this issue is some unknown processing. The manipulation with an unknown input leads to a array index vulnerability. Using CWE to declare the problem leads to CWE-129. The product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array. Impacted is availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-40097 since 04/09/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. The technical details are unknown and an exploit is not available.

Upgrading to version 0.30.0-rc3 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch ffd31ac0a87e03b0224cb8363094bfe602242888 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• smallstep

Name

• certificates

Version

• 0.30.0-rc1
• 0.30.0-rc2

License

• open-source

Website

• Product: https://github.com/smallstep/certificates/

CPE 2.3info

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CPE 2.2info

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