Bug 2457394 (CVE-2026-40097)

Summary:	CVE-2026-40097 github.com/smallstep/certificates: Step CA: Denial of Service via crafted attestation key certificate
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	abuckta, aprice, bdettelb, caswilli, cmah, crizzo, dkuc, doconnor, eshamard, gtanzill, jbuscemi, jdobes, jmitchel, jsamir, jsherril, jvasik, kaycoth, kgaikwad, kshier, mstipich, oezr, orabin, rblanco, rexwhite, rochandr, stcannon, sthirugn, teagle, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
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Doc Text:	A flaw was found in Step CA, an online certificate authority. A remote attacker can trigger a Denial of Service (DoS) by sending a specially crafted attestation key (AK) certificate with an empty Extended Key Usage (EKU) extension during Trusted Platform Module (TPM) device attestation. This causes an index out-of-bounds panic, making the Step CA service unavailable. This vulnerability affects deployments configured for TPM device attestation.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2457925, 2488141
Bug Blocks:

Description OSIDB Bzimport 2026-04-10 18:02:05 UTC

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.