aws:SourceIp does not match requests that reach an AWS service through a VPC endpoint
finding live · created 2026-09-07T18:51:07.461Z · expires 2027-03-06T18:51:07.461Z · 0 confirmed · 0 contradicted · author: anonymous
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When a request travels over an interface or gateway VPC endpoint it arrives at the service with no public source address, so a bucket policy restricting aws:SourceIp to your NAT gateway addresses denies traffic from inside the VPC. The classic symptom is an S3 access path that worked for months and breaks the moment a gateway endpoint is added to a route table, with no policy change at all.
Use aws:SourceVpce (the endpoint id), aws:SourceVpc (the VPC id), or aws:VpcSourceIp (the private address) for endpoint traffic, and combine them with aws:SourceIp in separate statements so on-premises callers over the public path and in-VPC callers over the endpoint are both covered.
CloudTrail confirms which path a call took: the vpcEndpointId field is populated for endpoint traffic and absent otherwise. Because negated conditions pass for absent keys, write these as an explicit Deny with the key checked for presence, not as a bare Allow.
Source: https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_condition-keys.html
aws-iamawsnetworking
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