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CVE-2026-56725 – Unauthenticated Denial of Service – Zammad ≤ 7.0.1

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Summary

CVE-2026-56725 is a high-severity (CVSS 8.7) denial-of-service vulnerability in Zammad, the open-source web-based helpdesk and customer support system. An unauthenticated attacker can repeatedly send POST requests to the OTRS Import Controller’s import_check endpoint to block Zammad’s application worker processes, degrading or fully denying service to a production instance.

Technical details

  • Root cause: the import_check and import_status actions of the OTRS Import Controller are missing the setup_done_response authentication guard that other controller actions in Zammad carry, allowing them to execute on fully configured, production Zammad instances without any authentication.
  • Trigger condition: an attacker sends a POST request to /api/v1/import/otrs/import_check. The action then attempts to reach a blank/unconfigured OTRS endpoint and enters a retry loop with sleep intervals of roughly 30 and 45 seconds between attempts.
  • Attack vector: network, no authentication or prior account required; only the target hostname is needed, and a valid CSRF token can be trivially obtained from any prior GET response to the instance.
  • Impact: each request costs the attacker almost nothing but blocks a Zammad request worker for approximately 115 seconds. A small number of requests per second is sufficient to saturate the Puma worker pool, causing the application to become unresponsive to legitimate users for as long as the traffic continues.

Affected software

  • Zammad versions ≤ 7.0.1 are vulnerable.
  • Fixed in Zammad 7.0.2 and later.

Severity

  • CVSS v4.0 Score: 8.7 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to Zammad 7.0.2 or later, which adds the missing authentication guard to the import_check and import_status actions.
  • If patching is not immediately possible: restrict or block unauthenticated access to /api/v1/import/otrs/import_check and /api/v1/import/otrs/import_status at a reverse proxy or web application firewall, and monitor for repeated/abnormal POST traffic to these paths as an indicator of ongoing exploitation attempts.

References

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