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 agentmods add skills/thejefflarson/soundcheck/broken-access-controlnpx skills add thejefflarson/soundcheck --skill broken-access-controlgit clone --depth 1 https://github.com/thejefflarson/soundcheckWhat 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 | $0.00062 | $0.00837 |
| Opus 5 | $0.00031 | $0.00418 |
| Sonnet 5 | $0.00012 | $0.00167 |
| Haiku 4.5 | $0.00006 | $0.00084 |
Grade A, and why
broken-access-control 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 2d 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 — 64 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Broken Access Control Security Check (A01:2025)
What this checks
Protects against unauthorized resource access caused by missing ownership checks or
role enforcement. Exploitation leads to horizontal/vertical privilege escalation.
For SSRF (server-side request forgery), see the dedicated ssrf skill.
Vulnerable patterns
- Resource lookup by caller-supplied identifier with no ownership predicate before the row is returned, mutated, or acted on
- Privileged or admin route mounted with no role check at the route/controller declaration
- Ownership check that runs after the resource has already been fetched and consumed by downstream logic
- Ownership failure that responds with a distinct "forbidden" status, leaking that the resource exists
Fix immediately
Flag the vulnerable code and explain the risk. Then suggest a fix that establishes these properties:
- Every resource lookup by caller-supplied identifier is gated before the resource is returned, mutated, or acted on. The gate binds the row to the authenticated caller — an ownership predicate for per-instance access, or a role predicate for role-scoped access. The check can live in a handler, interceptor, filter, annotation, decorator, or middleware — anywhere, as long as it runs before the data is used.
- Privileged routes enforce role membership through a reusable, centrally-declared
mechanism (middleware, filter chain, annotation, decorator, policy) attached at
the route or controller declaration. Ad-hoc
if role != "admin"checks inside handler bodies are brittle — they can be forgotten on a new route and they're invisible at a glance. - Ownership failures return an indistinguishable "not found" response (HTTP 404). Returning 403 leaks that the resource exists. Role-missing failures on a privileged route may still return 403 — the route itself is public knowledge, so only the instance-level check needs to hide behind 404.
Translate these principles to the audited file's language and framework. Use the documented authorization or policy mechanism for that stack; do not invent ad-hoc checks in handler bodies.
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.
- 2d ago First seen · 64 lines · 62 tokens per session scan A ae9b73891ef6
broken-access-control is a skill published in the GitHub repository thejefflarson/soundcheck (20 stars, last pushed 1mo ago), licensed MIT. It adds 62 tokens to every session and 837 once invoked, about $0.0003 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 2026-08-30.
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