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.
npx skills add UnboundCompute/security-agent-skills --skill auditing-file-upload-and-content-handlinggit clone --depth 1 https://github.com/UnboundCompute/security-agent-skillsWrote 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.
[](https://agentmods.dev/skills/unboundcompute/security-agent-skills/auditing-file-upload-and-content-handling)<a href="https://agentmods.dev/skills/unboundcompute/security-agent-skills/auditing-file-upload-and-content-handling"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/auditing-file-upload-and-content-handling/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/unboundcompute/security-agent-skills/auditing-file-upload-and-content-handling"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/auditing-file-upload-and-content-handling.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00207 | $0.02175 |
| Opus 5 | $0.00103 | $0.01087 |
| Sonnet 5 | $0.00041 | $0.00435 |
| Haiku 4.5 | $0.00021 | $0.00217 |
Grade A, and why
auditing-file-upload-and-content-handling scanned grade A with 0 findings 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 12d 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 138 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Auditing file upload and content handling: when the type one layer trusts another layer contradicts
A file upload becomes a vulnerability when the layer that decides a file's type disagrees with the layer that later serves or parses it. The upload validator trusts the extension or the declared content-type; the web server sniffs the bytes, or the storage path serves it inline, or a parser acts on embedded content, and the two disagreements meet in the attacker's favor. You audit it by resolving how the type is decided at upload and how the file is served and parsed afterward, then finding where those two views diverge. The strongest false-positive killers live in the serve layer: a no-execute sandboxed origin with a forced download, or a server-side re-encode, neutralizes the content regardless of its bytes. The client-side DOM sink and the archive-extraction write primitive have their own skills; this skill owns the upload-to-serve-or-parse decision.
When to use
- You are reviewing an upload endpoint, its type validation, where files are stored, and how they are served.
- A file's bytes, declared type, name, or embedded content reach a parser, a renderer, or a served location.
- You want to know whether an uploaded file executes or is parsed dangerously somewhere downstream.
Scope check
Audit only applications you own or are authorized to assess, and upload a crafted file only to a system in scope, a stored active file can execute against real users. Adjudicate on the validation, the storage, and the serve path. If you can't name the authorization, stop.
The loop
- Resolve the type-decision layer and the serve behavior first. Determine how the upload decides the file's type (an extension check, a declared content-type, a magic-byte sniff, or a combination) and how the file is served afterward (inline or as an attachment, from the app origin or a separate no-execute origin, with what content-type). The bug is a divergence between these two, so establish both before judging any single check.
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.
- 12d ago First seen · 138 lines · 207 tokens per session scan A e586092829c3
auditing-file-upload-and-content-handling is a skill published in the GitHub repository UnboundCompute/security-agent-skills (5 stars, last pushed 3d ago), licensed MIT. It adds 207 tokens to every session and 2,175 once invoked, about $0.0010 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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