SeaweedFS: Path traversal in the S3 and Iceberg REST gateways allows cross-bucket access

Overview

Summary

The S3 API gateway and the Iceberg REST catalog gateway construct their routers with mux.NewRouter().SkipClean(true). With path cleaning disabled, a .. segment inside the URL survives routing, so a request such as:

GET /bucket-A/../evil-bucket/key

is matched as bucket=bucket-A, object=../evil-bucket/key. The captured object key is then joined into a filer path with util.JoinPath (S3) / path.Join (Iceberg), which collapse the .. server-side, so the actual read or write lands in evil-bucket.

The captured path variables were never validated for traversal segments before reaching the handlers, so bucket isolation depended on downstream checks rather than on the path itself.

Impact

• With authentication disabled (enableAuth=false): direct cross-bucket read and write. An object key containing .. resolves to and operates on a different bucket than the one named in the request path.
• With authentication enabled (enableAuth=true): an authorization confused-deputy. IAM evaluates the policy against the mux {bucket} variable (bucket-A) in iam.authRequestWithAuthType, while the I/O is performed against the traversed target (evil-bucket). A principal authorized for one bucket can therefore reach objects in another bucket it has no grant for. This breaks tenant isolation.

The same class of traversal applies to the Iceberg REST catalog's {prefix}, {namespace}, and {table} path variables.

%2e%2e-encoded and ..\ (backslash) variants are equivalent, because gorilla/mux URL-decodes captured variables and NormalizeObjectKey folds \ to / before the path is used.

Affected components

• S3 API gateway (weed s3, and the S3 endpoint embedded in weed server)
• Iceberg REST catalog gateway

Affected versions

All releases prior to 4.30.

Patched version

4.30 and later.

Proof of concept

With a bucket evil-bucket containing secret.txt, and a caller that only has (or needs no) access to bucket-A:

GET /bucket-A/../evil-bucket/secret.txt HTTP/1.1
Host: <gateway>

The response returns the contents of evil-bucket/secret.txt. The encoded form GET /bucket-A/%2e%2e/evil-bucket/secret.txt behaves identically.

Remediation

Upgrade to SeaweedFS 4.30 or later. The fix adds a validation middleware to both gateway routers that rejects any captured path variable containing a . or .. segment, a NUL byte, an embedded slash/backslash in single-segment slots, or an empty captured value, before any handler runs.

Workarounds

For deployments that cannot upgrade immediately, place a reverse proxy in front of the gateway that normalizes the request path and rejects requests whose path contains .., %2e%2e, or backslash sequences. Note that disabling auth removes the only remaining barrier, so do not rely on enableAuth=false deployments being protected by anything.

Resources

• Fix: https://github.com/seaweedfs/seaweedfs/pull/9687 (commit dd1b428)

Credits

Reported responsibly by Denis Abashkin (@dadbravo).

Affected packages

• github.com/seaweedfs/seaweedfs < 0.0.0-20260526080459-dd1b4287899e

Remediation

Upgrade to a patched release:

• github.com/seaweedfs/seaweedfs 0.0.0-20260526080459-dd1b4287899e