Windmill is an open-source developer platform used internally for managing code, APIs, background jobs, workflows, and user interfaces. In versions 1.634.6 and earlier, a security vulnerability (CVE-2026-26964) exists that allows any authenticated workspace member to retrieve Slack OAuth client secrets via the GET /api/w/{workspace}/workspaces/get_settings API endpoint. Normally, sensitive workspace settings such as OAuth client secrets should only be accessible to workspace administrators. However, due to a legacy implementation detail where the Slack OAuth client secret was stored as a plain value rather than using variable indirection, it was not included in the redaction logic applied to non-admin users. Consequently, non-admin users receive the full secret instead of a redacted placeholder. This exposure constitutes an information disclosure vulnerability categorized under CWE-200. The vulnerability does not permit unauthorized modification or denial of service but compromises confidentiality by leaking OAuth credentials that could be used to impersonate or access Slack integrations. The vulnerability requires the attacker to be an authenticated workspace member but does not require any additional user interaction. The issue was addressed and fixed in Windmill version 1.635.0 by properly redacting the Slack OAuth client secret for non-admin users. There are no known exploits in the wild at this time, and the CVSS v3.1 base score is 2.7, reflecting low severity due to limited impact and exploitation requirements.

The primary impact of this vulnerability is the unauthorized disclosure of Slack OAuth client secrets to any authenticated workspace member who is not an administrator. This exposure could allow malicious insiders or compromised user accounts to misuse Slack OAuth credentials, potentially enabling unauthorized access to Slack APIs, impersonation of the workspace in Slack integrations, or unauthorized data access through Slack apps. While the vulnerability does not allow direct modification of Windmill settings or disruption of services, the leaked credentials could be leveraged in broader attack scenarios against Slack workspaces integrated with Windmill. Organizations relying on Windmill for internal development and automation workflows that integrate with Slack are at risk of credential leakage, which could lead to lateral movement or data exfiltration within their Slack environment. The impact is limited to organizations using vulnerable versions of Windmill and having Slack integrations configured. Since exploitation requires authenticated access, external attackers without credentials cannot exploit this vulnerability directly. However, the risk remains significant in environments with many users or where user accounts may be compromised.

Organizations should upgrade Windmill to version 1.635.0 or later, where this vulnerability has been fixed by properly redacting Slack OAuth client secrets for non-admin users. Until upgrading, administrators should restrict workspace membership to trusted users only and monitor access logs for suspicious API calls to the /api/w/{workspace}/workspaces/get_settings endpoint. Additionally, rotating Slack OAuth client secrets after upgrading is recommended to invalidate any potentially exposed credentials. Implementing strict access controls and auditing on Slack integrations can help detect and prevent misuse of leaked credentials. Organizations should also review their internal policies regarding the sharing of sensitive configuration data and consider additional encryption or secret management solutions to protect OAuth credentials. Regular security assessments and user privilege reviews will reduce the risk of insider threats exploiting this vulnerability.