CVE-2026-71191
Description
A flaw was found in the S3API middleware of OpenStack Swift. The SigV4 presigned URL implementation does not require that semantic x-amz-* headers be included in the request signature. An attacker who obtains a presigned PUT URL can inject unsigned headers such as X-Amz-Copy-Source to copy objects from the signer's storage, bypassing the intended scope of the presigned URL authorization. The attacker needs prior knowledge of the target project_id, container name, and object name.
Statement
Red Hat OpenStack Platform (RHOSP) and Red Hat OpenStack Services on OpenShift (RHOSO) ship openstack-swift and are affected by this vulnerability. In default RHOSO deployments, the s3api filter is included in the active proxy-server pipeline, and the s3_acl option is not explicitly set (defaulting to false). SigV4 presigned URL requests are processed through the S3API middleware and are vulnerable. All RHOSP (13, 16.2, 17.1) and RHOSO (18.0) deployments with s3api enabled in the pipeline are affected.
Mitigation
If S3 API compatibility is not required, remove the s3api filter from the proxy-server pipeline in proxy-server.conf. This completely eliminates the attack surface. If S3 API is required, restrict the distribution and scope of presigned PUT URLs as an operational control, and apply the upstream patch when available. There is no configuration-only workaround that fully mitigates this issue while keeping S3 API functionality enabled.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.2 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | High | N/A | N/A |
| Integrity Impact | Low | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
Red Hat CVSS v3 Score Explanation
Network-accessible S3API endpoint. No auth needed (presigned URLs are for unauthenticated access). Low complexity (just add unsigned header). C:H (read any object accessible to signer). I:L (metadata injection, PUT semantics change). A:N (no availability impact).
Acknowledgements
Upstream acknowledges Christian Schwede (NVIDIA) as the original reporter.
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