S3 Bucket Policy Project 10: Org-Only आणि Presigned URL Pitfalls

By Ravindra Bagale, trainer · LinkedIn · Last updated: 28 October 2026

1. Story

Tara Krishnan (चेन्नई) व Camille Dupont (Paris) — member accounts only.

2. PrincipalOrgID का?

हे का लागतं?

50 account list fragile. PrincipalOrgID = o-xxxx; IAM Allow अजून लागतं.

• एक condition
• IAM still
• Service carve-out
• No Referer auth

3. Policy

हे काय आहे?

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AllowOrgPrincipals",
      "Effect": "Allow",
      "Principal": "*",
      "Action": ["s3:GetObject", "s3:ListBucket"],
      "Resource": [
        "arn:aws:s3:::rb-org-shared-ap-south-1",
        "arn:aws:s3:::rb-org-shared-ap-south-1/*"
      ],
      "Condition": {
        "StringEquals": { "aws:PrincipalOrgID": "o-xxxxxxxxxx" }
      }
    },
    {
      "Sid": "DenyOutsideOrg",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": [
        "arn:aws:s3:::rb-org-shared-ap-south-1",
        "arn:aws:s3:::rb-org-shared-ap-south-1/*"
      ],
      "Condition": {
        "StringNotEquals": { "aws:PrincipalOrgID": "o-xxxxxxxxxx" },
        "Bool": { "aws:PrincipalIsAWSService": "false" }
      }
    }
  ]
}

Line-by-line

1. Org Allow.
2. Deny outside + service carve.
3. Service bool.
4. Real org id.
5. IAM still.
6. External deny.

4. Presigned + Referer pitfall

# BAD idea (do not rely on this)
# Condition StringLike aws:Referer https://myportal.example.com/*
# A curl -H 'Referer: https://myportal.example.com/' bypasses the "protection".

# Presigned URL — still valid if leaked, until expiry, regardless of Referer
aws s3 presign s3://rb-org-shared-ap-south-1/guide.pdf --expires-in 60
# https://rb-org-shared-ap-south-1.s3.amazonaws.com/guide.pdf?X-Amz-Algorithm=...

5. CLI

कसं करायचं (step by step)

ORG=o-xxxxxxxxxx
aws s3api put-bucket-policy --bucket rb-org-shared-ap-south-1 --policy file://org-only.json

# ALLOW — member account role
aws s3 ls s3://rb-org-shared-ap-south-1/ --profile member
# guide.pdf

# DENY — external account
aws s3 ls s3://rb-org-shared-ap-south-1/ --profile external
# AccessDenied

6. Allow/deny

Allow: member. Deny: external. Referer forge ≠ security.

7. Multi-industry

Landing zones, retail org, hospital, gaming.

8. AccessDenied debugging आणि Policy Simulator

AccessDenied क्रम: BPA → bucket Deny → IAM Allow → KMS → VPCe → ACL. Simulator BPA/VPC/KMS miss करू शकतो — खऱ्या CLI ने test.

# Decode
aws s3api get-bucket-policy --bucket BUCKET --query Policy --output text | python3 -m json.tool
aws s3api get-public-access-block --bucket BUCKET
aws iam simulate-principal-policy --policy-source-arn ARN \
  --action-names s3:GetObject --resource-arns arn:aws:s3:::BUCKET/key.txt
aws cloudtrail lookup-events --lookup-attributes AttributeKey=EventName,AttributeValue=GetObject --max-items 5

9. Lab: org-only + referer

Org block नसेल तर ap-south-1 (Mumbai). आधी budget alert.

कसं करायचं (step by step)

1. Org policy.
2. Allow/deny.
3. Presign myth.
4. Write myth bust.

Cleanup (billing थांबवा)

1. Cleanup.
2. Key hygiene.

10. सामान्य errors आणि fixes

प्रत्येक row = खरी चूक. Panic करण्याआधी fix वाचा.

11. Troubleshooting checklist

1. Region + endpoint.
2. Policy + BPA.
3. Lab user.
4. Sid binary search.
5. CloudTrail.
6. KMS test.
7. VPCe path.
8. Lock cleanup.

12. FAQ

13. Interview Q&A

14. Tips — English, मराठी आणि हिंदी

15. Policy save करण्याआधी checklist

1. Business rule एका वाक्यात.
2. Allow vs Deny-unless; Deny wins.
3. ARN shapes.
4. Condition keys.
5. BPA first.
6. Allow+deny plan.
7. Cleanup plan.
8. json.tool.

16. Policy Simulator walkthrough

Simulator identity/resource typos साठी चांगला; BPA/VPCe/KMS miss होऊ शकतात. नंतर खऱ्या path वरून CLI.

1. Simulator → user/role.
2. Action + ARN.
3. Include bucket policy.
4. CLI confirm.
5. Mismatch → layers.

17. Copy-paste runbook

# 0) Region + names
export AWS_REGION=ap-south-1
export BUCKET=rb-lab-$(date +%s)-ap-south-1

# 1) Create + show BPA
aws s3api create-bucket --bucket $BUCKET --region $AWS_REGION \
  --create-bucket-configuration LocationConstraint=$AWS_REGION
aws s3api get-public-access-block --bucket $BUCKET || true

# 2) Validate + apply policy
python3 -m json.tool policy.json >/dev/null
aws s3api put-bucket-policy --bucket $BUCKET --policy file://policy.json
aws s3api get-bucket-policy --bucket $BUCKET --query Policy --output text | python3 -m json.tool | head

# 3) Allow test + Deny test (fill per project)
# ... project-specific curls / aws s3 cp ...

# 4) Cleanup
aws s3 rm s3://$BUCKET --recursive || true
aws s3api delete-bucket-policy --bucket $BUCKET || true
aws s3api delete-bucket --bucket $BUCKET

18. Industry story bank

वरील प्रत्येक project एक industry story वापरतो. इतर industries मध्ये फक्त bucket/principal/Condition बदला.

• Healthcare: SSE-KMS + OrgID + MFA.
• Fintech: IP + HTTPS + OAC.
• EdTech: OAC only.
• Logistics: VPCe.
• Media: Object Lock.
• Retail: prefix public read.
• SaaS: prefix homes.
• Gov: OrgID + MFA + Lock.

19. AccessDenied debugging flowchart

1. Error code + request id.
2. Bucket + region.
3. BPA.
4. Explicit Deny.
5. Conditions.
6. KMS key policy.
7. OAC id.
8. VPCe path.
9. Simulator + CLI.
10. Support last.

20. PR review checklist

• Valid JSON.
• Required fields.
• No open write.
• Tests.
• Cleanup.

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