CVE-2026-44937 Overview
CVE-2026-44937 affects SUSE Rancher Fleet, a GitOps-based continuous delivery controller for Kubernetes clusters. The vulnerability allows remote attackers to forge webhook requests when an unauthenticated webhook is configured. Successful exploitation can trigger denial of service conditions or force downgrade attacks against other repositories managed by the Fleet controller. The issue is tracked under [CWE-918] Server-Side Request Forgery and carries a CVSS 4.0 score of 8.3.
Critical Impact
Remote unauthenticated attackers can forge webhook payloads to disrupt GitOps pipelines and downgrade repository state across Fleet-managed clusters.
Affected Products
- SUSE Rancher Fleet 0.15 before 0.15.2
- SUSE Rancher Fleet 0.14 before 0.14.6
- SUSE Rancher Fleet 0.13 before 0.13.11
- SUSE Rancher Fleet 0.12 before 0.12.5
Discovery Timeline
- 2026-07-06 - CVE-2026-44937 published to NVD
- 2026-07-06 - Last updated in NVD database
Technical Details for CVE-2026-44937
Vulnerability Analysis
Rancher Fleet exposes a webhook endpoint that receives repository change notifications from upstream Git providers. When the webhook is configured without authentication, the controller accepts inbound requests without verifying the origin or integrity of the payload. Attackers on the network can craft webhook messages that impersonate legitimate Git server callbacks.
The forged requests are processed by the Fleet reconciliation loop as if they originated from a trusted source. This behavior maps to [CWE-918] Server-Side Request Forgery, since the controller acts on attacker-influenced input to initiate downstream operations against repositories it manages.
Root Cause
The root cause is missing authentication and origin validation on the webhook receiver. Fleet trusts the payload structure without verifying a shared secret, HMAC signature, or mutual TLS identity. Any client capable of reaching the webhook endpoint can submit events that the controller treats as authoritative.
Attack Vector
An attacker locates a reachable Fleet webhook endpoint and sends crafted POST requests referencing repositories tracked by the controller. By supplying manipulated commit references, the attacker can force Fleet to reconcile against an older commit, effectively downgrading application state across clusters. Repeated forged events can also saturate the reconciliation queue, producing a denial of service against unrelated repositories managed by the same Fleet instance.
The vulnerability mechanism is described in the Rancher Fleet GitHub Security Advisory. No verified public exploit code is available.
Detection Methods for CVE-2026-44937
Indicators of Compromise
- Unexpected POST requests to Fleet webhook endpoints originating from IP addresses outside your Git provider's published ranges.
- Fleet controller logs showing reconciliation events referencing commit SHAs that predate the current repository HEAD.
- Sudden spikes in webhook processing volume without corresponding activity in the upstream Git provider.
Detection Strategies
- Correlate Fleet controller webhook receipts with Git provider audit logs to identify events lacking a matching upstream push.
- Alert on repository state transitions that move HEAD backward in commit history on managed clusters.
- Monitor Kubernetes audit logs for GitRepo and Bundle object churn that does not align with legitimate CI/CD activity.
Monitoring Recommendations
- Forward Fleet controller logs and Kubernetes API server audit logs to a central SIEM for correlation with network telemetry.
- Track ingress traffic to Fleet webhook services and baseline normal source addresses.
- Enable alerting on any deployment rollback across Fleet-managed workloads.
How to Mitigate CVE-2026-44937
Immediate Actions Required
- Upgrade Fleet to a patched release: 0.15.2, 0.14.6, 0.13.11, or 0.12.5 depending on the deployed branch.
- Audit all Fleet webhook configurations and remove any that are unauthenticated.
- Restrict network access to the webhook endpoint using ingress policies or an authenticating reverse proxy.
Patch Information
SUSE has released fixed versions in the 0.12.5, 0.13.11, 0.14.6, and 0.15.2 branches. Full remediation details are provided in the Rancher Fleet GitHub Security Advisory GHSA-jmf4-m7j9-g72r. Operators should apply the upgrade that matches their current minor version and verify controller pods are running the patched image.
Workarounds
- Configure a webhook secret on every GitRepo resource and require signature verification on inbound requests.
- Place the Fleet webhook behind an authenticating gateway that validates source IP and HMAC signatures before forwarding traffic.
- Isolate the Fleet controller namespace with a NetworkPolicy that only permits webhook traffic from known Git provider egress ranges.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
