step-ca Has Improper Authorization Check for SSH Certificate Revocation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2025-66406: 0.16% estimated exploitation activity in the next 30 days; percentile 5.45 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An authorized attacker can bypass authorization checks and revoke any SSH certificate issued by Step CA by using a valid revocation token. Details Step CA users can obtain SSH certificates from a few provisioners. The SSHPOP provisioner allows revocation of the SSH certificate (preventing future certificate renewals) using a token. Due to a missing validity check, this token could be used to revoke any SSH certificate issued by the CA. To create a token, an attacker must have access to the CA endpoint and a valid SSH certificate, meaning they were already authorized to obtain an SSH certificate. The attacker must also know the serial number of the certificate they want to revoke. Impact There is no way to mitigate this attack. It is recommended to update to v0.29.0 or newer. Fix In v0.29.0, the token validation logic was strengthened to bind each token to a specific SSH certificate serial number. Acknowledgements This issue was identified and reported by Gabriel Departout and…

Published by the source

3 Dec 2025, 16:27 UTC

Last modified by the source

20 Dec 2025, 02:28 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-j7c9-79x7-8hpr

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# Patch Next advisory brief: CVE-2025-66406

Advisory: step-ca Has Improper Authorization Check for SSH Certificate Revocation
IDs: CVE-2025-66406, GHSA-j7c9-79x7-8hpr
Record: https://patchnext.com/advisories/cve-2025-66406 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/smallstep/certificates 0.29.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/smallstep/certificates: affected <= 0.28.4; fixed in 0.29.0

## Suggested inspection (read-only)
- Go github.com/smallstep/certificates: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/smallstep/certificates.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-j7c9-79x7-8hpr (GitHub-reviewed advisory GHSA-j7c9-79x7-8hpr lists affected ranges: Go github.com/smallstep/certificates >=0 <=0.28.4)

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