CVE-2026-51773: OpenStack glance_store SSRF Vulnerability

CVE-2026-51773 Overview

CVE-2026-51773 is a Server-Side Request Forgery (SSRF) vulnerability in the VMware datastore driver of OpenStack glance_store. The _retry_request function fails to validate the destination host before attaching sensitive authentication headers to outbound requests. An authenticated attacker can supply a crafted image location URI that points to an attacker-controlled external server. The vulnerable code then forwards VMware vCenter credentials to that remote host. This flaw is classified under CWE-918: Server-Side Request Forgery.

Critical Impact
Authenticated attackers can exfiltrate VMware vCenter authentication headers by redirecting Glance image retrieval requests to arbitrary external servers.

Affected Products

OpenStack glance_store library
Deployments using the VMware vSphere datastore backend
OpenStack Glance image service instances configured with VMware storage

Discovery Timeline

2026-09-25 - CVE-2026-51773 published to the National Vulnerability Database (NVD)
2026-09-30 - Last updated in NVD database

Technical Details for CVE-2026-51773

Vulnerability Analysis

The glance_store library brokers image data between OpenStack Glance and various storage backends, including VMware vSphere datastores. The VMware driver uses an internal _retry_request helper to perform HTTP operations against the configured vCenter endpoint. These requests carry authentication headers derived from the service's vCenter credentials.

The function does not verify that the request target matches the configured vCenter host before attaching those headers. When image location metadata contains a URL, the driver follows it without host allow-listing. An authenticated OpenStack user who can register or update an image location can therefore cause the Glance service to send vCenter credentials to any reachable host.

Root Cause

The root cause is missing destination host validation in _retry_request. Authentication headers are attached unconditionally rather than scoped to the trusted vCenter endpoint. This is a classic SSRF pattern [CWE-918] where user-controlled input influences a server-initiated request without proper allow-listing.

Attack Vector

Exploitation requires low-privilege authenticated access to the OpenStack API. The attacker registers or modifies a Glance image whose location URI points to an external host under their control. When the VMware driver processes the location through _retry_request, it issues an authenticated HTTP request to the attacker's server. The attacker captures the authentication headers from inbound request logs and reuses them against the real vCenter.

For technical proof-of-concept details, see the GitHub CVE-2026-51773 Details and the GitHub PoC Repository.

Detection Methods for CVE-2026-51773

Indicators of Compromise

Outbound HTTPS connections from Glance API hosts to destinations other than the configured vCenter endpoint.
Glance image records whose location or locations metadata reference external URLs or unexpected hostnames.
Unexpected Authorization, Cookie, or vCenter session headers appearing in traffic to non-vCenter hosts.

Detection Strategies

Audit the Glance image catalog for location URIs that do not resolve to the organization's vCenter infrastructure.
Inspect glance-api logs for _retry_request calls targeting unexpected hostnames or returning anomalous status codes.
Correlate Glance service account network flows with the allow-listed vCenter IP ranges and alert on deviations.

Monitoring Recommendations

Enable egress filtering on Glance API nodes and log every denied connection for review.
Monitor vCenter authentication logs for session reuse from unexpected source IP addresses.
Alert on new or modified Glance image records containing non-datastore URL schemes submitted by non-administrative tenants.

How to Mitigate CVE-2026-51773

Immediate Actions Required

Upgrade glance_store to a fixed release once published by the OpenStack security team.
Restrict Glance image creation and location-setting privileges to trusted operators using policy rules.
Rotate vCenter credentials configured in the Glance VMware driver if exploitation is suspected.

Patch Information

At the time of publication, no vendor advisory URL is listed in the NVD record. Operators should monitor the OpenStack security advisories and the glance_store project release notes for a patched version addressing CVE-2026-51773. Technical references are available in the GitHub CVE-2026-51773 Details.

Workarounds

Disable the VMware datastore driver in glance-api.conf if the backend is not required.
Enforce network egress policies that permit Glance API nodes to reach only the sanctioned vCenter endpoint.
Remove or restrict the set_location and add_image_location API permissions for untrusted tenants via Glance policy configuration.

bash

# Example Glance policy restriction to limit image location updates to admins
# /etc/glance/policy.yaml
"add_image_location": "role:admin"
"set_image_location": "role:admin"
"get_image_location": "role:admin"