Articles July 27, 2026 3 min read

Stopping AP Fraud at the Source: How To Prevent Vendor Fraud in Accounts Payable

Advisory

Outsourced Accounting Systems and Services (OASyS)

Vendor fraud in the accounts payable (AP) process is no longer a niche concern. It is a universal risk that touches finance, operations and firm governance. For controllers, CFOs, and operations leaders, prevention starts with understanding where modern processes are vulnerable and how those weaknesses translate into financial and operational exposure.

Where Companies Are Most Exposed Today

Email-based vendor communications, decentralized approval workflows, and increasing reliance on third-party vendors all create gateways for fraud. The most common exposure points include:

Vendor master data changes: Fraudsters target weak controls around bank detail updates. They often impersonate legitimate vendors through business email compromise schemes.
Invoice submission channels: Email invoices without validation layers are easy to duplicate or manipulate.
High-volume, low-touch environments: Automation without sufficient oversight can quickly lead to fraud and errors.

Common Breakdowns in Process and Controls

Even well-run organizations have gaps that fraud exploits:

Insufficient segregation of duties: The same individual can create or modify vendors and approve payments.
Lack of verification procedures: Changes to vendor banking details are not independently confirmed.
Overreliance on trust-based relationships: Longstanding vendors are assumed to be low-risk, reducing scrutiny.
Manual exceptions: Urgent or “one-off” payments bypass standard controls.

The Financial and Operational Fallout

Vendor fraud compounds across the organization:

Direct financial loss: Payments made to fraudulent accounts are often unrecoverable.
Cash flow disruption: Duplicate or erroneous payments interfere with proper cash flow reporting.
Audit and compliance exposure: Weak controls can trigger findings, penalties, or restatements.
Time and money: Fraud investigations consume financial and legal resources, taking away from core activities.

Eight Steps To Reduce Vendor Fraud Risk

Reducing vendor fraud risk requires a combination of process control, technology, and leadership alignment:

Strengthen vendor onboarding and changes: Require multi-factor verification for any vendor master updates, especially banking details. Call-back procedures using known contacts, not those provided in the request, are highly effective.
Enforce segregation of duties: Ensure no single individual controls vendor setup, invoice approval and payment execution.
Standardize and secure invoice intake: Move away from open email channels and toward structured portals.
Abnormality detection: Use analytics to flag unusual payment patterns, duplicate invoices or changes in vendor behavior. Modern AP tools can expose these risks in real time.
Strengthen approval workflows: Have data (e.g., historical payments, contracts) available within approval processes so decision-makers can spot irregularities quickly.
Conduct periodic audits of vendor master data: Regularly review vendor records for duplicates, inactive vendors or recent changes to critical fields.
Train beyond AP: Fraud prevention is not just an AP responsibility. Approvers and executives should understand common fraud tactics. Cybersecurity awareness across the organization closes the human gap.
Efficient incident response plan: Clearly define roles across finance, legal, IT and banking partners to contain and investigate incidents quickly.

Vendor fraud risk is ultimately a company-wide issue, not just a transactional one. Organizations that have deliberate controls over AP functions are better positioned to protect cash, maintain integrity and support leadership decisions.

Protect Your AP Process Before Fraud Finds It

Withum’s Outsourced Accounting Systems and Services (OASyS) Team helps organizations build accounts payable processes with the control’s fraud can’t slip through segregation of duties, secure invoice intake, vendor master oversight and real-time payment visibility.

Contact Us

Not sure where your AP process is exposed? Reach out to our Outsourced Accounting Systems and Services (OASyS) Team to find out.

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