MalformedPolicyDocument
AWS MalformedPolicyDocument means the IAM policy document is malformed and includes syntax or structural errors (HTTP 400).
Last reviewed: February 26, 2026|Editorial standard: source-backed technical guidance
What Does Malformed Policy Document Mean?
IAM rejected the policy before attachment/update because the rendered document violates JSON or IAM policy grammar requirements, so authorization changes never take effect.
Common Causes
- -Policy JSON is syntactically invalid or contains malformed statement structure.
- -Unsupported IAM policy elements, condition keys, or action/resource combinations are used.
- -Template interpolation introduces broken ARNs, escaping issues, or duplicate keys.
- -Policy version/effect/principal blocks are missing required fields.
How to Fix Malformed Policy Document
- 1Validate policy JSON and IAM grammar with linters before API submission.
- 2Correct the first parser/validation error and re-run full policy validation.
- 3Test policy using IAM simulation tools before attaching or updating in production.
- 4Render templates to final JSON and diff against known-good policy patterns.
Step-by-Step Diagnosis for Malformed Policy Document
- 1Capture exact IAM parser/validator message and the failing statement path.
- 2Inspect rendered final policy JSON, not just template source.
- 3Validate actions, resources, principals, and condition keys against IAM grammar/docs.
- 4Run policy simulation to confirm corrected document behavior after syntax fixes.
Policy Grammar and JSON Structure Validation
- -Validate rendered policy JSON for syntax and required top-level elements (example: malformed
Statementarray or invalidVersionblock). - -Check action/resource/condition compatibility with IAM grammar (example: unsupported condition key under selected action).
Template Rendering and Simulation Checks
- -Inspect final rendered policy artifacts instead of templates (example: interpolation creates invalid ARN with missing account segment).
- -Run policy simulation and static linting before apply (example: parser passes JSON but simulation fails due to malformed principal/resource pairing).
How to Verify the Fix
- -Re-apply policy and confirm IAM accepts the document.
- -Validate effective permissions with IAM simulation tools.
- -Ensure no new policy parse errors appear in change logs.
How to Prevent Recurrence
- -Adopt policy-as-code linting and simulation in CI.
- -Version-control policy templates with strict schema checks.
- -Require review gates for IAM policy grammar changes.
Pro Tip
- -keep a versioned IAM change ledger with request IDs and simulated policy decisions so rollback and root-cause analysis stay deterministic.
Decision Support
Compare Guide
HTTP 400 vs 422: Bad Request vs Unprocessable Content
Fix API payload issues faster by using 400 for malformed syntax and 422 for semantic validation failures, so clients correct format before business rules.
Playbook
CORS Error Fix Playbook (Preflight / Origin / Credentials)
Use this playbook to separate browser-enforced cross-origin policy failures from server-side CORS header and route defects and apply strict origin and credential controls safely.
Playbook
Validation Failure Playbook (400 / 422 / INVALID_ARGUMENT)
Use this playbook to separate malformed-request failures from semantic validation failures, then fix request contracts without broad server-side bypasses.
Official References
Provider Context
This guidance is specific to AWS services. Always validate implementation details against official provider documentation before deploying to production.