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-s3-object-ownership-trustgit 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-s3-object-ownership-trust)<a href="https://agentmods.dev/skills/unboundcompute/security-agent-skills/auditing-s3-object-ownership-trust"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/auditing-s3-object-ownership-trust/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-s3-object-ownership-trust"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/auditing-s3-object-ownership-trust.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 | $0.00175 | $0.01932 |
| Opus 5 | $0.00088 | $0.00966 |
| Sonnet 5 | $0.00035 | $0.00386 |
| Haiku 4.5 | $0.00017 | $0.00193 |
Grade A, and why
auditing-s3-object-ownership-trust 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 11d 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 — 134 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Auditing S3 object-ownership trust: when the object, not the bucket, decides access
Object stores let access be decided in more than one place, and that is where ownership trust breaks. A bucket policy is the central control most teams reason about, but each object also has an owner and, unless disabled, its own ACL, and a cross-account upload can land an object owned by the uploader rather than the bucket owner. The result is objects the bucket owner cannot fully control, ACLs that grant access the bucket policy meant to deny, and public grants riding on individual objects under a bucket that looks private. When a bucket receives objects from more than one principal, central governance is an assumption, not a fact. You audit these by checking who owns each object, whether object ACLs are still in force, and whether any object grants access the bucket policy did not intend.
When to use
- A bucket receives objects from more than one principal, including cross-account or third-party writers.
- Access is meant to be governed centrally by the bucket policy, but object ACLs may still be enabled.
- Cross-account writes may land objects the bucket owner does not own or cannot fully read or control.
Scope check
Audit object ownership only in buckets and accounts you own or are authorized to assess, on non-production data. Confirming access reads or controls real objects, so stay inside the authorized bucket and treat any object contents as sensitive within scope. If you can't name the authorization, stop.
The loop
-
Establish the intended access model first. Name who should read and control the objects in this bucket and how it is meant to be enforced: central bucket policy, single owner. This is the false-positive killer: a bucket with ownership enforced to the bucket owner and object ACLs disabled, governed only by the bucket policy, is correct. Name the intended model, then check whether ownership and ACLs match it.
-
Determine object ownership across writers. For objects written by more than one principal, confirm who owns each. A cross-account upload can retain the uploader's ownership, leaving objects the bucket owner cannot fully control. Check whether bucket-owner-enforced ownership is set so every object is owned centrally, or whether uploader ownership persists.
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.
- 11d ago First seen · 134 lines · 175 tokens per session scan A 2ad136743427
auditing-s3-object-ownership-trust is a skill published in the GitHub repository UnboundCompute/security-agent-skills (5 stars, last pushed 3d ago), licensed MIT. It adds 175 tokens to every session and 1,932 once invoked, about $0.0009 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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