What breaks when S3 permissions are granted too broadly or with wildcard actions?

Why This Matters for Security Teams

Broad S3 permissions are not just an access-design issue. They turn object storage into a high-value control gap where one compromised token can read, write, delete, or enumerate far more than intended. That is especially dangerous when IAM policies use wildcard actions or resource scopes, because investigators cannot quickly separate legitimate automation from unsafe access. NHI Management Group notes that 97% of NHIs carry excessive privileges, which is exactly the kind of condition that makes storage abuse hard to detect early, as reflected in the Ultimate Guide to NHIs — Key Challenges and Risks.

For AWS, the problem compounds because S3 permissions are often inherited by service accounts, CI/CD pipelines, and application roles that were meant to be narrow but drifted over time. When a policy allows s3:* or overly broad object and bucket actions, a single credential can cross from routine operations into destructive behaviour. That weakens auditability, inflates blast radius, and undermines least privilege in a way that is difficult to reverse after deployment. In practice, many teams discover this only after an object-loss event, not during policy review.

How It Works in Practice

Good S3 governance starts with separating read, write, list, and destructive actions, then scoping each to the smallest feasible bucket, prefix, or lifecycle boundary. The issue with wildcard actions is that they often hide multiple capabilities inside one permission statement. A role granted s3:* may be able to list sensitive buckets, overwrite data, delete objects, or change bucket configuration even when only upload access was intended. The same risk appears when a policy uses wildcard resources across environments, because a test workload can unexpectedly reach production data.

Practitioners should treat S3 permissions as workload identity and intent questions, not just IAM syntax. That means reviewing what the service or agent is supposed to do, then mapping those tasks to explicit actions and conditions. The OWASP Non-Human Identity Top 10 is useful here because it frames excessive privilege as an NHI risk, while NIST control guidance in SP 800-53 Rev. 5 Security and Privacy Controls reinforces least privilege and access restriction as core defensive requirements.

• Replace s3:* with explicit actions such as GetObject, PutObject, and ListBucket only when justified.
• Scope object access to exact bucket names and prefixes instead of broad resource wildcards.
• Separate read-only roles from write or delete roles so a single compromise cannot do everything.
• Use conditions to narrow access by encryption requirements, network path, or account context where supported.

For incident response, explicit permissions also make it easier to answer who could delete what, when, and from where. That matters because S3 abuse often involves chaining one broad permission into another, then using the same credential to exfiltrate or destroy data. NHIMG research on the Codefinger AWS S3 ransomware attack shows how storage permissions can become a direct destruction path when access is too permissive. These controls tend to break down when teams rely on shared roles across many workloads because the resulting privilege overlap masks the true blast radius.

Common Variations and Edge Cases

Tighter S3 permissions often increase policy maintenance overhead, requiring organisations to balance precision against operational drift. That tradeoff is real, especially when many applications need different bucket prefixes, temporary upload paths, or batch jobs that behave differently across environments.

One common edge case is third-party automation. If a vendor integration needs temporary object write access, current guidance suggests giving it a narrowly scoped role rather than broad bucket access, but there is no universal standard for every workflow shape yet. Another exception involves data pipelines that must enumerate and transform many objects. In those cases, the safer pattern is explicit bucket and prefix scope plus separate delete permissions, not one wildcard statement for convenience.

Another practical wrinkle is that some teams overcorrect by creating too many roles, which makes reviews harder and can encourage shadow reuse of powerful credentials. The right balance is clear separation of duties, short-lived credentials where possible, and a permission model that can be explained in an audit without hand-waving. NHI Management Group’s broader guidance on NHI sprawl and exposure in the Ultimate Guide to NHIs — Key Challenges and Risks remains relevant here because over-permissioned storage roles are often part of a larger identity hygiene problem.

Related resources from NHI Mgmt Group

• What breaks when MCP tool permissions are scoped too broadly?
• What breaks when agent access is granted too broadly at build time?
• What breaks when wildcard .onion certificates are used too broadly?
• What breaks when service account impersonation is granted too broadly?