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Payroll webhooks to accounting: signature, replay, and data in transit

Published on 2026-04-164 min readFlorian

The payroll webhook is a forgotten surface

Each month, webhooks leave the payroll tool for accounting, HRIS, ERP. They carry amounts, identities, sometimes partial IBANs.

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What must exist

  • HMAC signature verified on the receiving side, not just emitted;
  • replay protection (timestamp + nonce);
  • TLS in transit required, not optional;
  • sender-side log of every webhook sent with status.
  • The concrete test

    Replay a signed webhook two hours later. If the receiver accepts it, that's a design issue, not just a setting.

    For HR & Payroll vendors

    CleanIssue specializes in security reviews for HR, payroll, and recruiting software. If you're building an HRIS, payroll tool, or ATS and want an external review of your exposure before a client audit or security questionnaire, see our offer for HR & Payroll vendors.

    Go further

    Related articles

    Three adjacent analyses to keep exploring the same attack surface.

    Sources

    Written by Florian
    Reviewed on 2026-04-16

    Editorial analysis based on official vendor, project, and regulator documentation.

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