Title

Chat Identity Link Hijacking — Attacker Can Silently Map Their Slack/Discord Identity to Any Authenticated Budibase User's Account

Severity

High — CVSS 3.1: AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N = 7.3

Affected Product

• Product: Budibase
• Version: 3.37.2 (introduced in this version)
• Component: packages/server/src/api/controllers/ai/chatIdentityLinks.ts
• Endpoint: GET /api/chat-links/:instance/:token/handoff

Vulnerability Type

• CWE-352: Cross-Site Request Forgery
• CWE-284: Improper Access Control

Vulnerability Description

GET /api/chat-links/:instance/:token/handoff is a public endpoint (no auth required) that performs a permanent, state-changing operation: it binds an external chat identity (Slack/Discord/MS Teams) to an authenticated Budibase user account, with no consent UI and no CSRF protection.

The session token in the URL is created by the attacker (from their own /link slash command) and embeds the attacker's externalUserId. When an authenticated Budibase victim visits the URL, their account is silently and permanently linked to the attacker's Slack/Discord identity. The server responds with "Authentication succeeded." — no indication of what was linked.

Route Registration

// packages/server/src/api/routes/chat.ts:22
router.get(
  "/api/chat-links/:instance/:token/handoff",
  controller.handoffChatLinkSession   // registered in publicRoutes — zero auth middleware
)

Vulnerable Controller (full function)

// packages/server/src/api/controllers/ai/chatIdentityLinks.ts:61–110
export async function handoffChatLinkSession(
  ctx: UserCtx<void, string, { instance: string; token: string }>
) {
  const token = resolveToken(ctx.params.token)
  const session = await sdk.ai.chatIdentityLinks.getChatIdentityLinkSession(token)
  if (!session) {
    throw new HTTPError("Link token is invalid or has expired", 400)
  }
  assertSessionMatchesInstance({ workspaceId: session.workspaceId, instance: ctx.params.instance })

  if (!ctx.isAuthenticated) {
    // Unauthenticated: set return URL cookie, redirect to login
    // After login, same URL is visited again → attack completes silently
    utils.setCookie(ctx,
      `/api/chat-links/${ctx.params.instance}/${token}/handoff`,
      "budibase:returnurl",
      { sign: false }  // ← unsigned cookie, but not an open redirect
    )
    ctx.redirect("/builder/auth/login")
    return
  }

  const currentGlobalUserId = getCurrentGlobalUserId(ctx)
  const consumedSession = await sdk.ai.chatIdentityLinks.consumeChatIdentityLinkSession(token)

  // ↓↓↓ THE VULNERABLE WRITE — no consent check, no CSRF token ↓↓↓
  await sdk.ai.chatIdentityLinks.upsertChatIdentityLink({
    provider: consumedSession.provider,
    externalUserId: consumedSession.externalUserId,  // ← ATTACKER's Slack ID
    externalUserName: consumedSession.externalUserName,
    teamId: consumedSession.teamId,
    globalUserId: currentGlobalUserId,   // ← VICTIM's Budibase user ID
    linkedBy: currentGlobalUserId,
  })

  ctx.type = "text/html"
  ctx.body = renderLinkSuccessPage()  // ← "Authentication succeeded." — no disclosure to user
}

--

Step 1 — Attacker triggers /link in Slack

Attacker types /link to the Budibase Slack bot. Budibase server creates a Redis session:

Redis key: chatIdentityLinkSession:tok_xxxxxxxxxxxxxxxx

Redis value (exact structure from ChatIdentityLinkSession interface):

{
  "token": "tok_xxxxxxxxxxxxxxxx",
  "tenantId": "acme",
  "workspaceId": "ws_abc123",
  "provider": "slack",
  "externalUserId": "UA12345678",
  "externalUserName": "attacker",
  "teamId": "T_ACME_SLACK",
  "createdAt": "2026-05-02T10:00:00.000Z",
  "expiresAt": "2026-05-02T10:10:00.000Z"
}

Slack DM sent privately to attacker:

Link your Slack account to continue chatting with this agent.
https://budibase.company.com/api/chat-links/ws_abc123/tok_xxxxxxxxxxxxxxxx/handoff

Key observation: This URL embeds the attacker's own externalUserId inside the token. The attacker has full control over which identity gets linked.

Step 2 — Attacker forwards URL to victim

Attacker posts in the company Slack:

@admin please click this to connect your Budibase account for AI agent access:
https://budibase.company.com/api/chat-links/ws_abc123/tok_xxxxxxxxxxxxxxxx/handoff

Step 3 — Victim clicks link (authenticated)

HTTP Request (victim's browser):

GET /api/chat-links/ws_abc123/tok_xxxxxxxxxxxxxxxx/handoff HTTP/1.1
Host: budibase.company.com
Cookie: budibase:session=VICTIM_SESSION

HTTP Response:

HTTP/1.1 200 OK
Content-Type: text/html

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Authentication succeeded</title>
  </head>
  <body>
    <p>Authentication succeeded.</p>
    <script>
      if (window.opener && !window.opener.closed) {
        try { window.opener.focus(); window.close() } catch (error) {}
      }
    </script>
  </body>
</html>

The victim sees "Authentication succeeded." with no mention of Slack, no mention of attacker, no mention of what capabilities were granted.

CouchDB global-db document written immediately after (exact structure from upsertChatIdentityLink):

{
  "_id": "chatidentitylink_acme_slack_T_ACME_SLACK_UA12345678",
  "tenantId": "acme",
  "provider": "slack",
  "externalUserId": "UA12345678",
  "globalUserId": "ro_global_us_VICTIM_ADMIN_ID",
  "linkedAt": "2026-05-02T10:00:42.000Z",
  "linkedBy": "ro_global_us_VICTIM_ADMIN_ID",
  "externalUserName": "attacker",
  "teamId": "T_ACME_SLACK",
  "createdAt": "2026-05-02T10:00:42.000Z",
  "updatedAt": "2026-05-02T10:00:42.000Z"
}

The mapping is now permanent. externalUserId = UA12345678 (attacker) → globalUserId = ro_global_us_VICTIM_ADMIN_ID (victim).

Step 4 — Attacker impersonates victim via AI agent

Attacker sends any message to the Budibase Slack bot from their own account (UA12345678).

The chat handler resolves the identity:

// packages/server/src/api/controllers/webhook/chatHandler.ts:421
const existingLink = await sdk.ai.chatIdentityLinks.getChatIdentityLink({
  provider: AgentChannelProvider.SLACK,
  externalUserId: "UA12345678",     // ← attacker's Slack ID
  teamId: "T_ACME_SLACK",
})
// existingLink.globalUserId = "ro_global_us_VICTIM_ADMIN_ID"

const linkedUser = await getGlobalUser("ro_global_us_VICTIM_ADMIN_ID")
// All agent tool calls now execute with victim admin's permissions

The attacker can now ask the agent:

"Show me all rows in the Customers table"
"Trigger the 'Send Invoice' automation for customer ID 42"
"What files are in the knowledge base?"

Each request runs with the victim admin's identity and permissions. The victim has no indication this is happening.

Step 3b — Variant: Victim Not Yet Authenticated

If the victim is not currently logged in when they click the URL:

HTTP Request:

GET /api/chat-links/ws_abc123/tok_xxxxxxxxxxxxxxxx/handoff HTTP/1.1
Host: budibase.company.com

HTTP Response:

HTTP/1.1 302 Found
Location: /builder/auth/login
Set-Cookie: budibase:returnurl=%2Fapi%2Fchat-links%2Fws_abc123%2Ftok_xxxxxxxxxxxxxxxx%2Fhandoff; Path=/

After the victim logs in, the browser follows the return URL and the attack completes identically to Step 3.

Remediation

Minimum Fix — Add Consent Page

Convert the handoff to a two-step flow:

GET  /api/chat-links/:instance/:token/handoff
  → Show consent page: "You are linking your Budibase account to
    [externalUserName]'s Slack identity ([provider]).
    This allows them to interact with AI agents as you. [Confirm] [Cancel]"

POST /api/chat-links/:instance/:token/handoff  (with CSRF token)
  → Perform the upsertChatIdentityLink() write

Moving the write to POST removes it from publicRoutes, making Budibase's existing CSRF middleware apply automatically.

Credits,
Vishal Kumar B
https://github.com/VishaaLlKumaaRr

References

• packages/server/src/api/routes/chat.ts:22 — public route registration
• packages/server/src/api/controllers/ai/chatIdentityLinks.ts:61–110 — full vulnerable controller
• packages/server/src/sdk/workspace/ai/chatIdentityLinks.ts:135–165 — session creation (embeds attacker's externalUserId)
• packages/server/src/sdk/workspace/ai/chatIdentityLinks.ts:202–247 — upsertChatIdentityLink (permanent write)
• packages/server/src/api/controllers/webhook/chatHandler.ts:421 — identity resolution during agent message handling
• packages/server/src/ai/tools/budibase/automations.ts — automation trigger capability
• packages/server/src/ai/tools/budibase/rows.ts — row read/write capability
• packages/types/src/sdk/chatIdentityLinks.ts — session + link type definitions
• CWE-352: Cross-Site Request Forgery
• CWE-284: Improper Access Control