CVE-2026-55874 is a high-severity (CVSS 7.7) Path Traversal vulnerability in github.com/seaweedfs/seaweedfs. A fix is available for github.com/seaweedfs/seaweedfs — see the affected versions and patch details below.
SeaweedFS: Path traversal in the S3 gateway X-Amz-Copy-Source header allows cross-bucket object read
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55874.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-55874 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
github.com/seaweedfs/seaweedfsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The SeaweedFS S3 API gateway did not reject .. path segments in the X-Amz-Copy-Source header used by CopyObject and UploadPartCopy. The request URL path was hardened against traversal in 4.30 (CVE-2026-54917), but the copy-source header was only checked for emptiness, so a .. segment in the copy source survived into the server-side filer path and resolved into a different bucket.
Impact
A confused-deputy authorization bypass that breaks bucket isolation. IAM evaluates the caller's policy against the bucket named in the request URL (the destination the caller owns), while the copy reads its source from the traversed target bucket. An identity scoped to a single bucket (Read + Write on one bucket it controls) can therefore read any object in any bucket on the instance and land the result in its own bucket.
For example, a caller authorized only for bucket-a issues a CopyObject into bucket-a with copy source bucket-a/../<victim-bucket>/<key>; the gateway reads <victim-bucket>/<key> and writes it to the attacker-controlled destination, from which the caller reads it normally. UploadPartCopy (CopyObjectPartHandler) is affected by the same vector.
Affected versions
All releases prior to 4.34. The 4.30 fix for CVE-2026-54917 hardened the request URL path but not the X-Amz-Copy-Source header.
Patched version
4.34 and later.
Remediation
Upgrade to 4.34 or later. The fix validates the copy-source bucket and object key with the same IsValidBucketName / IsValidObjectKey guards already applied to the request URL, rejecting traversal segments before the handler runs, and applies the same check to UploadPartCopy.
Workaround
No configuration workaround. For deployments that cannot upgrade immediately, front the gateway with a reverse proxy that rejects requests whose X-Amz-Copy-Source header contains .., %2e%2e, or backslash sequences.
References
- Fix: https://github.com/seaweedfs/seaweedfs/pull/9929 (commit b44cf51fe931bd75aa4d37ae766bea90d7f85ccd)
Credit
Reported responsibly by @47Cid.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/seaweedfs/seaweedfs | all versions | 0.0.0-20260612000715-b44cf51fe931go get github.com/seaweedfs/seaweedfs@v0.0.0-20260612000715-b44cf51fe931 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/seaweedfs/seaweedfs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/seaweedfs/seaweedfs to 0.0.0-20260612000715-b44cf51fe931 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55874 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Important: This flaw in SeaweedFS allows an authenticated attacker to bypass intended access controls within the S3 API gateway. By crafting a malicious `X-Amz-Copy-Source` header with "dot-dot" path segments, an attacker with limited bucket access can read objects from other unauthorized buckets. This could lead to…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-55874 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 4 on RHEL 9 | cryostat/cryostat-storage-rhel9:4.2.0-22 | RHSA-2026:68333 |
Frequently Asked Questions
Is CVE-2026-55874 in your dependencies?
Find it across Go, including transitive dependencies.