How should banks replace SMS OTP for high-risk transactions?

Why This Matters for Security Teams

SMS OTP still appears convenient, but it is a weak control for high-risk banking actions because it protects the login moment, not the payment decision. Attackers can intercept text messages, abuse SIM swap fraud, or trick customers into handing over one-time codes during a live session. For a bank, that means the approval channel is often easier to compromise than the account itself.

Current guidance in NIST Cybersecurity Framework 2.0 and the NHIMG Ultimate Guide to NHIs — Why NHI Security Matters Now both point to stronger, context-aware controls when the action itself carries fraud exposure. That is especially relevant for beneficiary changes, large transfers, device enrolment, and profile resets. In those cases, the bank needs assurance that the approval is bound to the transaction details and the authenticated customer session, not just a reusable code.

Practitioners also need to account for operational reality: SMS depends on telecom trust, user discipline, and message delivery timing, all of which degrade under attack. In practice, many security teams encounter OTP weaknesses only after a fraud case or account takeover has already occurred, rather than through intentional control testing.

How It Works in Practice

Replacing SMS OTP for high-risk transactions usually means moving to step-up authentication that is transaction-bound and harder to relay. The best pattern is evolving, but the common design is to challenge the customer inside a trusted channel, such as the bank app, after the transaction details are displayed for explicit approval. That approval should be cryptographically tied to the amount, beneficiary, and timestamp so it cannot be reused for a different payment.

For banks, stronger options include in-app push approval, software tokens, device biometrics, and passkeys where the risk model supports them. The key is not the factor alone, but whether the factor proves possession of a trusted device and binds the response to the exact action being authorised. That aligns with the broader direction in the NHIMG Top 10 NHI Issues, where weak secret handling and poor lifecycle control routinely create avoidable exposure.

• Use step-up only for elevated risk events, not every login.
• Bind approval to transaction context, including payee and amount.
• Prefer short-lived, session-specific approval tokens over reusable OTPs.
• Apply fraud signals, device posture, and behaviour analytics before issuing the challenge.
• Log the full decision path for dispute handling and controls testing.

Where possible, banks should also combine beneficiary confirmation and cooling-off controls for new payees, because account takeover often succeeds through social engineering rather than direct cryptographic compromise. This approach fits the intent of Ultimate Guide to NHIs — Key Challenges and Risks, which shows how long-lived, overexposed identity artifacts amplify downstream abuse. These controls tend to break down when the customer must operate on an untrusted device with poor app integrity because the bank can no longer trust the approval channel itself.

Common Variations and Edge Cases

Tighter step-up controls often increase friction, so banks have to balance fraud reduction against customer abandonment and support costs. That tradeoff is real, especially for high-volume retail payments where even small delays can trigger complaints. Current guidance suggests risk-based prompting rather than blanket challenge on every action, because overuse trains customers to approve reflexively.

There is no universal standard for this yet, but a practical pattern is to reserve the strongest challenge for beneficiary additions, first-time device enrolment, high-value transfers, and changes to contact details. For lower-risk events, a lighter control may be enough if paired with anomaly detection and strong session security. Banks should also plan for accessibility, travel, device loss, and fallback recovery, because a secure flow that customers cannot complete will generate workarounds.

One recurring edge case is step-up on a compromised device. If malware or session hijacking already exists on the phone, in-app approval may still be vulnerable unless the bank validates device integrity, app attestation, and transaction signing. For that reason, the control set should be reviewed alongside the broader 2024 ESG Report: Managing Non-Human Identities, which highlights how often identity protections fail once attackers gain a foothold. In practice, SMS OTP is usually retired first in the channels where fraud loss is already visible, not where architecture teams would prefer to start.

Related resources from NHI Mgmt Group

• When does MFA create enough assurance for high-risk access?
• How should security teams reduce phishing risk in high-value access paths?
• Why do consumer banking flows need step-up authentication for high-risk actions?
• Why do ephemeral credentials still leave risk in machine access models?