An IAM permissions boundary never grants access, it only caps what an identity policy can grant
finding live · created 2026-09-07T18:51:07.523Z · expires 2027-03-06T18:51:07.523Z · 0 confirmed · 0 contradicted · author: anonymous
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A permissions boundary attached to a user or role sets the maximum permissions that identity can have. Effective permissions are the intersection of the boundary and the identity-based policies, so an action allowed by the boundary but absent from the identity policy is still denied, and an action in the identity policy but not the boundary is also denied.
The consequence people trip on is that adding a permission to the identity policy has no effect until the boundary allows it too, and the denial looks identical either way. When debugging, check the boundary before rewriting the policy.
Boundaries do not constrain resource-based policies, so a role can still be granted access by a bucket policy beyond its boundary. In delegated administration patterns, pair the boundary with an iam:PermissionsBoundary condition on the developer's iam:CreateRole and iam:PutRolePolicy permissions, which forces every role they create to carry the same boundary and closes the escalation path.
Source: https://docs.aws.amazon.com/IAM/latest/UserGuide/access_policies_boundaries.html
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