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 xalgorix/xalgorix --skill implementing-gcp-vpc-firewall-rulesgit clone --depth 1 https://github.com/xalgorix/xalgorixWrote 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/xalgorix/xalgorix/implementing-gcp-vpc-firewall-rules)<a href="https://agentmods.dev/skills/xalgorix/xalgorix/implementing-gcp-vpc-firewall-rules"><img src="https://agentmods.dev/badge/skills/xalgorix/xalgorix/implementing-gcp-vpc-firewall-rules/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/xalgorix/xalgorix/implementing-gcp-vpc-firewall-rules"><img src="https://agentmods.dev/badge/skills/xalgorix/xalgorix/implementing-gcp-vpc-firewall-rules.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Server-Side Request Forgery · line 174 Code accesses a cloud instance metadata endpoint (e.g. 169.254.169.254). A single request can return temporary IAM credentials, making this a high-value SSRF target for credential theft.Fix: Remove access to cloud metadata endpoints unless strictly required. If metadata is needed, restrict it (e.g. IMDSv2 with hop limit) and never expose returned credentials.
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 | $0.00052 | $0.03237 |
| Opus 5 | $0.00026 | $0.01618 |
| Sonnet 5 | $0.00010 | $0.00647 |
| Haiku 4.5 | $0.00005 | $0.00324 |
Grade B, and why
implementing-gcp-vpc-firewall-rules scanned grade B 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 6d 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.
Cloud metadata endpointmediumServer-side request forgery
One request to 169.254.169.254 can return temporary IAM credentials.
--destination-ranges=169.254.169.254/32,8.8.8.8/32,8.8.4.4/32 \ Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
How it starts
The opening of the file, as written. The whole thing — 328 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Implementing GCP VPC Firewall Rules
When to Use
- When deploying new GCP workloads that require network-level access controls
- When auditing existing firewall configurations for overly permissive rules
- When implementing zero trust network segmentation within GCP VPC networks
- When responding to Security Command Center findings about open firewall rules
- When building hierarchical firewall policies across a GCP organization
Do not use for application-layer filtering (use Cloud Armor WAF), for DNS-based filtering (use Cloud DNS response policies), or for VPN/interconnect traffic filtering without understanding that VPC firewall rules apply to traffic within the VPC.
Common Misconfigurations & Verification
- Restrictive rule outranked by a default-allow: GCP evaluates lowest priority number first. A new
deny/tight rule at priority 1000 is overridden bydefault-allow-internal/default-allow-sshat lower numbers, or by an allow with a smaller priority value. List and sort by priority and delete the legacydefault-allow-*rules after validation. - Rule created but disabled: a
--disabledrule looks present but enforces nothing. Audit:gcloud compute firewall-rules list --filter="disabled=true". - Egress assumed denied: GCP's implied rule allows all egress (priority 65535). Without an explicit
deny-all-egressat 65534 plus scoped allows, exfiltration paths stay open. - Mutable network tags for sensitive rules: anyone with
compute.instances.setTagscan attach a tag and inherit an allow rule. Prefer--source-service-accounts/--target-service-accountsfor critical paths. - Flow logs off: you cannot validate which rule is actually matching or whether deletes are safe without
--enable-flow-logsanddisposition=DENIED/ALLOWEDqueries.
gcloud compute firewall-rules list --filter="direction=INGRESS AND sourceRanges=0.0.0.0/0" --sort-by=priority
gcloud compute firewall-rules describe default-allow-ssh --format='value(disabled,priority,sourceRanges.list())'
gcloud logging read 'resource.type="gce_subnetwork" AND jsonPayload.disposition="DENIED"' --limit=20
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.
- 6d ago First seen · 328 lines · 52 tokens per session scan B 413708cd0697
implementing-gcp-vpc-firewall-rules is a skill published in the GitHub repository xalgorix/xalgorix (971 stars, last pushed today), licensed Apache-2.0. It adds 52 tokens to every session and 3,237 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 1 finding (cloud metadata endpoint). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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