CVE-2026-93539 in Rancher
Summary
by MITRE • 09/28/2026
A vulnerability was discovered in Fleet's Git webhook receiver (the gitjob webhook service). When a webhook secret is not configured, incoming webhook requests are accepted without verification, and processing a request can change the spec.pollingInterval field of a matching GitRepo resource in any namespace. A caller with network access to the webhook service and no Kubernetes credentials can therefore alter GitRepo configuration outside
the namespaces they are authorized for. This only affects SUSE Rancher Fleet 0.16 before 0.16.2, older versions are not affected.
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Analysis
by VulDB Data Team • 09/28/2026
The vulnerability identified in SUSE Rancher Fleet prior to version 0.16.2 represents a critical authentication bypass within the Git webhook receiver service, specifically affecting the gitjob component. This flaw arises from an improper implementation of access control mechanisms where the system fails to validate incoming webhook requests when no secret is explicitly configured by the administrator. In secure software design, webhook endpoints must enforce strict verification protocols, typically using shared secrets or tokens, to ensure that only authorized sources can trigger state-changing operations. The absence of this validation allows any actor with network-level access to the service endpoint to interact with the API without providing valid credentials, effectively bypassing Kubernetes role-based access control policies that would normally restrict such actions.
From a technical perspective, the core issue lies in the handling of incoming HTTP requests directed at the webhook receiver. When the configuration for a webhook secret is missing or null, the application logic proceeds to process the request payload without performing any integrity checks or authentication steps. This lack of input validation and verification allows an attacker to craft malicious payloads that manipulate internal state variables within the Fleet management plane. Specifically, the vulnerability permits unauthorized modification of the spec.pollingInterval field associated with GitRepo resources. By altering this configuration parameter, an external actor can influence how frequently the system checks for updates in linked repositories, potentially disrupting synchronization processes or causing denial-of-service conditions through excessive polling cycles.
The operational impact of this flaw is significant due to its potential for lateral movement and privilege escalation within a Kubernetes cluster environment. Although the attacker does not possess valid Kubernetes credentials, they can still modify GitRepo configurations across any namespace on the cluster. This behavior violates the principle of least privilege and namespace isolation, as it allows an entity with only network access to affect resources outside their authorized scope. Such unauthorized modifications can lead to misconfigured deployment pipelines, unintended code execution if subsequent polling triggers deployments based on manipulated repository states, or general instability in the continuous delivery workflow managed by Fleet. The risk is particularly acute in multi-tenant environments where strict separation of duties between teams and namespaces is required for security compliance.
This vulnerability aligns with CWE-287, which describes Improper Authentication, as well as CWE-862, Missing Authorization, because the system fails to verify the identity of the requester and subsequently allows actions that should be restricted by role-based permissions. In terms of the MITRE ATT&CK framework for Kubernetes, this behavior corresponds to techniques involving unauthorized access to cluster resources via API server endpoints or webhook handlers, facilitating lateral movement within the container orchestration layer. The specific capability to alter configuration fields remotely without authentication highlights a failure in securing administrative interfaces against unauthenticated network actors.
To mitigate this vulnerability, organizations running SUSE Rancher Fleet versions 0.16 prior to 0.16.2 must upgrade immediately to version 0.16.2 or later where the issue has been resolved. In addition to upgrading, administrators should ensure that webhook secrets are properly configured and rotated regularly for all gitjob services. Implementing network-level restrictions such as IP whitelisting on the webhook endpoints can provide an additional layer of defense in depth, limiting exposure to trusted sources only. Furthermore, auditing existing configurations to verify that no critical webhook receivers operate without authentication mechanisms is essential to prevent exploitation by malicious actors who may have gained foothold within the internal network segment hosting these services.