Summary
If a malicious actor with prior access to an AWS environment has permission to modify the S3
Replication Service role access policy, they could abuse cross-account replication to exfiltrate
stolen data to an external bucket under their control. Moreover, when configured to replicate
to multiple buckets at once, and if logging is only scoped to specific buckets (as opposed to
being set to log "all current and future buckets"), then the S3 Replication Service only logs a putObject event to CloudTrail
for the first destination bucket. Thus, as long as the malicious actor's bucket isn't the first
replication destination, their activity wouldn't be logged in CloudTrail, and might go undetected.
Affected Services
S3
Remediation
None
Tracked CVEs
No tracked CVEs
References
https://www.vectra.ai/blogpost/abusing-the-replicator-silently-exfiltrating-data-with-the-aws-s3-replication-servicehttps://www.youtube.com/watch?v=9lvLboXE9tw
Contributed by https://github.com/korniko98
Disclosure Date
Tue, Oct 19th, 2021
Exploitablity Period
ongoing
Known ITW Exploitation
-
Detection Methods
Monitor for changes to Replication rules (e.g., via the S3BucketChangesAlarm alert in CloudWatch) and note any suspicious destinations.
Piercing Index Rating
-
Discovered by
Kat Traxler
