security-web

A guide to protecting server-side and API code using the OWASP Top 10, a widely used list of common web security risks. It covers access control, configuration, dependencies, encryption, injection, authentication, and related issues.

In plain words
What is it for?
Use it when writing or reviewing backend routes, adding dependencies, configuring TLS or security headers, preparing for launch, or investigating a security finding.
Why use it?
Backend code can expose private data or allow unwanted actions when security checks are missing or misconfigured. This guide gives developers a checklist and practical defenses for reviewing and hardening it.

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/kouroshez/coding-os/security-web
Any agent
npx skills add kouroshez/coding-os --skill security-web
Clone the repo
git clone --depth 1 https://github.com/kouroshez/coding-os

Made for: Claude Code, Codex.

Per session 128 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,879 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin original No closer match found 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 $0.00128 $0.04879
Opus 5 $0.00064 $0.02440
Sonnet 5 $0.00026 $0.00976
Haiku 4.5 $0.00013 $0.00488

Measured yesterday against content hash 25eb9c6b4f58, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

security-web 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 yesterday.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/csp-check.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

**Client-side `accept=`, JS MIME and JS size checks are UX only** — replayed in curl they vanish. Never drop a server-side check because the UI has one.
src/core/skills/security-web/SKILL.md · 268 lines

How it starts

The opening of the file, as written. The whole thing — 268 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Web / Backend Security — OWASP Top-10 (2025) + 2026 Practice

A practical playbook for hardening server-side code. Anchored on OWASP Top-10 (2025) — released November 2025, the current standard, replaces the 2021 list. Targets the project's stack — Go+Fiber business backend + Python+FastAPI AI adapter + PostgreSQL — with concrete code per category.

When to Use This Skill

  • Writing or reviewing any backend route / handler / middleware.
  • Adding a new third-party SDK / dependency.
  • Setting up TLS / HSTS / CSP headers.
  • Auditing existing code for OWASP categories.
  • Pre-launch security review.
  • Investigating a security incident or pentest finding.

For client-side mobile hardening, see security-mobile. For auth specifically, see auth-patterns.

OWASP Top-10 (2025) — Per Category

The full per-category walk-through with concrete defenses + code samples is in references/owasp-top-10.md. The skim summary, in 2025 ranking order:

ID Category 2021 → 2025 change Top defense
A01 Broken Access Control same #1 Default deny; use case asserts ownership; multi-tenant via Postgres RLS
A02 Security Misconfiguration ↑ from #5 to #2 Security headers; no DEBUG in prod; default admin paths protected; least-privilege containers
A03 Software Supply Chain Failures renamed + expanded from "Vulnerable & Outdated Components" (was #6) SBOM per release; pin commits not tags in CI; OIDC short-lived tokens; staged rollouts; MFA on registry/repo accounts
A04 Cryptographic Failures ↓ from #2 to #4 TLS 1.2+; Argon2id for passwords; SHA-256 for refresh-token hashing; KMS-encrypted PII
A05 Injection ↓ from #3 to #5 Parameterized queries everywhere; never concat user input into SQL/shell/templates
A06 Insecure Design ↓ from #4 to #6 Server-authoritative checks; idempotency; rate limiting; threat modeling
A07 Authentication Failures renamed (was "Identification and Authentication Failures") See auth-patterns skill
A08 Software or Data Integrity Failures same #8 No insecure deserialization; signed updates; pinned action SHAs
A09 Security Logging and Alerting Failures renamed (was "Monitoring") Auth events logged with request_id; alerts on anomalies; runbooks per alert
A10 Mishandling of Exceptional Conditions NEW in 2025 Catch at source; fail-closed transactions; centralized error handler; resource cleanup in finally

Read the full file on GitHub · 268 lines

Files

What ships with it

4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. yesterday First seen · 268 lines · 128 tokens per session scan A 25eb9c6b4f58

Subscribe to this mod's changes

security-web is a skill published in the GitHub repository kouroshez/coding-os (6 stars, last pushed yesterday), licensed Apache-2.0. It adds 128 tokens to every session and 4,879 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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