CVE-2026-26964: Windmill Information Disclosure Flaw

CVE-2026-26964 Overview

CVE-2026-26964 is an Information Disclosure vulnerability affecting Windmill, an open-source developer platform for internal code including APIs, background jobs, workflows, and UIs. The vulnerability allows non-admin users to obtain Slack OAuth client secrets through the workspace settings API endpoint, which should only be accessible to workspace administrators.

Critical Impact
Authenticated non-admin users can access Slack OAuth client secrets via the /api/w/{workspace}/workspaces/get_settings endpoint, potentially leading to unauthorized access to Slack integrations and OAuth token theft.

Affected Products

Windmill versions 1.634.6 and below

Discovery Timeline

2026-02-20 - CVE CVE-2026-26964 published to NVD
2026-02-20 - Last updated in NVD database

Technical Details for CVE-2026-26964

Vulnerability Analysis

This vulnerability stems from improper access control in Windmill's workspace settings retrieval functionality. The GET /api/w/{workspace}/workspaces/get_settings endpoint returns the slack_oauth_client_secret to any authenticated workspace member, regardless of their administrative privileges.

While it is expected behavior for non-admin users to see a redacted version of workspace settings (as some settings are necessary for the frontend to function correctly for all users), the Slack OAuth configuration should have been excluded from non-admin responses. This represents a legacy issue where the setting was stored as a plain value instead of using $variable indirection, and it was never added to the redaction logic.

Root Cause

The root cause is classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The vulnerability exists because the Slack OAuth client secret was stored as a plain value rather than using variable indirection, and the field was never added to the redaction logic that should strip sensitive fields for non-admin users when returning workspace settings.

Attack Vector

The attack is network-based and requires low complexity to exploit. An attacker needs to be an authenticated workspace member (non-admin) to access the vulnerable endpoint. The attack flow involves:

An authenticated non-admin user makes a GET request to /api/w/{workspace}/workspaces/get_settings
The API returns the full workspace settings including the slack_oauth_client_secret field
The attacker obtains the Slack OAuth client secret which can be used to impersonate the application's Slack integration

rust

 use hex;
 use sha2::{Digest, Sha256};
 use std::collections::{HashMap, HashSet};
+use strum::IntoEnumIterator;
 use uuid::Uuid;
-use strum::{IntoEnumIterator};
 use windmill_audit::audit_oss::{audit_log, AuditAuthorable};
 use windmill_audit::ActionKind;
 use windmill_common::db::UserDB;

Source: GitHub Commit Changes

Detection Methods for CVE-2026-26964

Indicators of Compromise

Unusual API requests to /api/w/{workspace}/workspaces/get_settings from non-admin users
Unexpected access patterns to workspace configuration endpoints
Slack OAuth token usage from unrecognized IP addresses or locations

Detection Strategies

Monitor API access logs for GET /api/w/{workspace}/workspaces/get_settings requests from non-administrative user accounts
Implement alerting on bulk or automated requests to workspace settings endpoints
Review Slack OAuth activity logs for signs of unauthorized application impersonation

Monitoring Recommendations

Enable detailed logging for all workspace settings API endpoints
Configure alerts for non-admin users accessing sensitive configuration endpoints
Monitor Slack integration activity for anomalous behavior or unauthorized access patterns

How to Mitigate CVE-2026-26964

Immediate Actions Required

Upgrade Windmill to version 1.635.0 or later immediately
Rotate all Slack OAuth client secrets that may have been exposed
Audit access logs to determine if the vulnerability was exploited
Review workspace user permissions and remove unnecessary access

Patch Information

Windmill has released version 1.635.0 which addresses this vulnerability. The fix ensures that slack_oauth_client_secret is properly stripped from the get_settings response for non-admin users. For detailed patch information, refer to the GitHub Security Advisory GHSA-f27g-j463-q85w and the GitHub Release v1.635.0.

Workarounds

Restrict workspace membership to only trusted users until the patch can be applied
Temporarily disable Slack integration if not critical to operations
Use network segmentation to limit access to Windmill API endpoints
Implement additional authentication layers for sensitive configuration endpoints

bash

# Upgrade Windmill to patched version
# Using Docker:
docker pull ghcr.io/windmill-labs/windmill:1.635.0

# Or update your deployment configuration to reference v1.635.0