What breaks when SAP RFC modules are reachable by low-privilege users?

Why This Matters for Security Teams

When SAP RFC modules are reachable by low-privilege users, the security boundary shifts from the user role to the function module itself. That is a high-risk design assumption because RFC exposure can let a caller reach business logic, data movement, or system actions that were never meant to be available through ordinary transaction access. The issue is not just authorization failure; it is trust being placed in the wrong layer.

This is especially important in environments that already struggle with over-permissioned identities and opaque service access. NHI Mgmt Group notes that 97% of NHIs carry excessive privileges, broadening the attack surface, and that visibility into service accounts is often poor. That pattern maps directly to SAP governance when RFC destinations, technical users, and interface accounts are not tightly scoped. The Ultimate Guide to NHIs — Key Challenges and Risks and the OWASP Non-Human Identity Top 10 both reinforce the same operational point: the risky unit is often the credentialed path, not the named user.

In practice, many security teams encounter RFC abuse only after a low-privilege account has already used a trusted function path to reach privileged behaviour.

How It Works in Practice

In SAP, an RFC-enabled function module is callable remotely if the technical and application controls allow it. If that module is poorly designed, the caller may be able to supply parameters that alter execution in unsafe ways, including data reads, writes, or indirect access to privileged operations. The problem becomes worse when the module performs authority checks inconsistently, relies on caller-controlled input, or delegates sensitive work to downstream logic without revalidating context.

Security teams should think in terms of interface trust, not just user trust. A low-privilege user can still become a meaningful threat if the RFC boundary accepts inputs that are interpreted as code, commands, object names, or routing instructions. That is why allowlisting specific RFC modules, enforcing strict input validation, and separating read-only integration functions from privileged business functions are core controls. SAP governance also needs review of who can create or modify RFC destinations, technical users, and background execution paths, because those objects often determine what the module can reach.

Useful practice usually includes:

• Allowlist only the RFC modules that are required for a business process.
• Disable or tightly restrict remote enablement for modules that were never meant for external invocation.
• Review S_RFC and related authorizations alongside the technical account used for execution.
• Log and monitor unusual RFC call patterns, especially from low-privilege users or non-interactive accounts.
• Treat ABAP injection risk as a code-level issue, not just a role design issue.

Current guidance suggests pairing SAP role review with broader NHI governance because interface credentials often outlive the people who requested them. The Ultimate Guide to NHIs highlights how long-lived, poorly rotated credentials amplify risk, which is the same failure pattern seen in overexposed SAP technical access. These controls tend to break down in heavily customized SAP landscapes because bespoke function modules, legacy integrations, and weak ownership make it difficult to prove which RFCs are actually safe.

Common Variations and Edge Cases

Tighter RFC control often increases operational overhead, requiring organisations to balance integration speed against security assurance. That tradeoff is real in SAP environments where business teams depend on older interfaces, third-party connectors, and custom ABAP logic that no one wants to break.

One common edge case is a module that appears harmless because it only exposes lookup or status functions, yet still returns sensitive records or reveals internal object names that can be chained into later abuse. Another is “temporary” access that becomes permanent because interface owners are unclear or because the business cannot identify which module maps to which process. In those cases, current guidance suggests treating every remotely enabled function as an attack surface until it is explicitly justified.

The other major exception is when low-privilege access is only part of the problem. If a compromised technical account, trusted connector, or batch job can invoke the same RFC path, then the exposure is no longer limited to human role design. That is why the OWASP Non-Human Identity Top 10 is relevant here, even though the issue sits inside SAP: the credentialed interface itself is the real control point. Best practice is evolving, but the safe default is simple: if an RFC module does not need to be remotely callable, it should not be.

Related resources from NHI Mgmt Group

• What breaks when organisations JIT users instead of permissions?
• What breaks when organisations manage human and machine privilege the same way?
• What breaks when access reviews do not keep up with privilege creep?
• What breaks when access recertification is designed only for human users?