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Introduction:
Modern security engineers face a mounting challenge: managing diverse workflows for phishing analysis, IDOR testing, security code audits, and incident response without reinventing the wheel each time. A new approach empowers AppSec teams to leverage the skills.sh ecosystem and the npx skills CLI to install battle-tested security skills directly into Claude Code, reducing redundant work and standardizing repeatable security testing methodologies.
Learning Objectives:
- Objective 1: Install and configure security-focused skills for Claude Code using the npx skills CLI and skills.sh directory.
- Objective 2: Deploy specific skills for IDOR testing, phishing analysis, incident response, and code audit workflows.
- Objective 3: Integrate a curated skills stack—leveraging Transilience AI Community Tools—into a reusable security pipeline.
You Should Know:
- Understanding the Agent Skills Ecosystem and Security Implications
The Agent Skills ecosystem allows AI tools like Claude Code to extend functionality through modular “skills”—typically `SKILL.md` files containing instructions, scripts, and workflows. The skills.sh platform aggregates these capabilities, enabling engineers to install them with a single command. However, this plug-and-play simplicity introduces supply chain risks. A comprehensive security audit conducted by Snyk identified that 36% of audited skills contained prompt injection vulnerabilities, with 1,467 malicious payloads detected in a study of the ToxicSkills supply chain. Before installing any skill, use security scanners such as skillrx (npx skillrx) or claude-skill-antivirus to assess trust levels (TRUSTED, CAUTION, RISKY, MALICIOUS).
Step‑by‑Step Guide to Verify and Install Security Skills
- Prerequisites: Ensure Node.js (v18+) is installed and the target project has a `.claude/skills/` directory.
- Pre‑install Scan: Run `npx skillrx add
` to review the skill’s code without execution.
3. Install Using npx skills CLI:
Install a specific skill from GitHub npx skills add <owner/repository> Example: install IDOR testing skill npx skills add timderbak/security-skills-toolkit
This command downloads the skill into `./.claude/skills/` and updates `skills-lock.json` for reproducibility.
4. Verify Installation: Check `.claude/skills/` for the skill folder and `claude-skills-vault` logs for any errors.
5. Invoke the Skill: In Claude Code, use natural language triggers such as “Run IDOR test on endpoint /api/users” or the skill’s defined slash command.
- Deploying a Phishing Analysis Skill for Automated Email Security Checks
Phishing analysis is a high-frequency task that benefits from automation. A Claude Code skill can automate header analysis, URL extraction, and reputation checks. The ecosystem provides skills that classify incidents, collect evidence, and construct response timelines—turning manual triage into a repeatable workflow.
Step‑by‑Step Guide: Phishing Analysis Workflow
1. Install a Phishing Analysis Skill:
npx skills add jeremylongshore/responding-to-security-incidents
This skill supports phishing classification, evidence collection, and remediation steps.
2. Run the Analysis:
- In Claude Code, upload an EML or raw email text.
- “Perform phishing analysis on this email. Extract headers, URLs, and calculate risk score.”
- Automate with Slash Commands: Create a custom `/phish` slash command by adding a `SKILL.md` in `.claude/skills/` with YAML frontmatter defining the trigger phrase.
- Result: Claude returns structured output: suspicious indicators, recommended containment, and next steps.
-
IDOR Testing and Security Code Audit Skills for OWASP Top 10
Insecure Direct Object References (IDOR) remain a critical flaw in web applications. Pre-built skills guide AI through multi-step authorization testing, identifying missing ownership checks. While early LLM‑based detection suffered from false positives, modern skills integrate context‑aware scanning that traces data flows and reduces erroneous findings.
Step‑by‑Step Guide: IDOR and API Security Testing
1. Install the IDOR Testing Skill:
npx skills add timderbak/security-skills-toolkit
This toolkit includes IDOR, Auth Bypass, BAC, and SSRF testing modules.
2. Configure Target:
- Open Claude Code in your codebase.
- Instruct: “Run IDOR skill against the API endpoint
GET /api/v1/users/{id}. Highlight endpoints where user ID comes from client without server‑side ownership validation.”
- Review Findings: The skill outputs vulnerable endpoints and recommends patches, such as adding `@PreAuthorize(“hasPermission(id, ‘USER_VIEW’)”)` in Spring or `authorize()` middleware in Express.
- Automate Remediation: Some skills generate patch diffs; apply via Claude’s “Apply Fix” feature.
-
Incident Response Playbooks and Threat Hunting with Transilience AI Tools
For structured incident response, the Transilience AI Community Tools suite provides a consolidated security testing suite with 26 skills covering the full penetration testing lifecycle—from reconnaissance to reporting. These skills integrate with DFIR workflows, cloud containers, blockchain security, and CVE risk scoring.
Step‑by‑Step Guide: Deploying Transilience AI Skills
1. Clone the Repository:
git clone https://github.com/transilienceai/communitytools.git cd communitytools/skills
2. Install Desired Skills:
- For DFIR: `cp -r dfir/ /path/to/project/.claude/skills/`
– For API security: `cp -r api-security/ /path/to/project/.claude/skills/`
3. Trigger a Threat Hunt:
“Using DFIR skill, analyze auth logs for failed logins followed by successful access from same IP. Provide timeline and containment steps.”
4. Chain Multiple Skills: Use the coordination skill to sequence vulnerability scanning, exploitation, and reporting.
- Hardening Supply Chain Security for AI Skills (Windows & Linux)
Given the rise of malicious packages targeting npm and the Agent Skills ecosystem, implement strict controls. Attackers have distributed encrypted backdoors and phishing toolkits with 95 versions, highlighting the need for runtime defense.
Step‑by‑Step Guide: Securing Your Skills Pipeline
- Linux/macOS:
1. Audit existing skills: `npx skilllens scan ~/.claude/skills`
- Install only trusted forks: Use `npx secure-skills add
` which scans for malicious content before installation. - Set repository allowlist: Configure `.skills-config.json` to permit only specific GitHub orgs.
– Windows (PowerShell as Administrator):
1. `Set-ExecutionPolicy RemoteSigned -Scope CurrentUser`
2. `npm install -g claude-skill-antivirus`
3. `claude-scan –path C:\Users\%USERNAME%\.claude\skills –report`
- CI/CD Integration:
Add to GitHub Actions: `- name: Scan Claude Skills; run: npx skillrx check ./.claude/skills`
- Bridging the Gap: From SAST to AI‑Driven Application Security
Traditional SAST tools struggle with business logic flaws like IDOR because they cannot understand authorization intent. Claude Code Security, powered by Claude Opus 4.6, found over 500 high‑severity vulnerabilities in production open‑source codebases by tracing data flows across files. However, treat it as an evolution of SAST—not a replacement for DAST, SCA, or runtime protection.
Step‑by‑Step Guide: Combining Skills with Traditional Scanning
- Run `npx skills add Anthropic/claude-code-security` (once available) to enable AI‑driven context analysis.
- Integrate results into your pipeline: Parse Claude’s JSON output into SARIF format for dashboarding.
- Automate remediation: Use skills to generate patch PRs, but enforce human review via branch protection.
-
Creating and Sharing Your Own Skills for Team‑Wide Consistency
To avoid rebuilding workflows, package your internal security processes as skills. Follow the Agent Skills open standard, which works across Claude Code, Cursor, and GitHub Copilot.
Step‑by‑Step Guide: Build a Custom Skill
1. Create folder: `.claude/skills/my-sec-audit/`
2. Write `SKILL.md`:
name: "security-audit" description: "Run OWASP Top 10 checks and produce report" triggers: ["audit security", "run OWASP check"] Steps: 1. List dependencies with known CVEs (<code>npm audit</code> or <code>safety check</code>) 2. Scan for hardcoded secrets (<code>gitleaks detect --source=.</code>) 3. Output findings with risk scoring
3. Test locally: Prompt Claude, “audit security in this codebase.”
4. Share via internal Git or upload to skills.sh directory.
What Undercode Say:
- Key Takeaway 1: Leveraging pre‑built security skills dramatically reduces repetitive work, but engineers must treat skill installation like any third‑party dependency—scan before trusting.
- Key Takeaway 2: The future of AppSec lies in hybrid AI‑human workflows: AI handles context‑aware detection and patch generation, while human teams focus on strategic validation and architecture.
The integration of AI‑driven skills into Claude Code represents a paradigm shift for security engineering. By adopting the skills.sh ecosystem and Transilience AI’s 26‑skill suite, teams can transition from ad‑hoc scripting to repeatable, documented workflows. However, the recent identification of 1,467 malicious payloads in the Agent Skills supply chain serves as a stark warning: automation must be paired with rigorous security hygiene. Use tools like skillrx and claude‑skill‑antivirus for pre‑install scanning, enforce allowlists, and treat every skill installation as a potential supply chain risk. As AI agents become central to security operations, the ability to curate, verify, and share skills will separate reactive teams from proactive ones.
Prediction:
Within 18 months, enterprise security teams will maintain internal “skill registries” with automated scanning and approval gates, mirroring modern software composition analysis for AI extensions. Organizations that fail to govern skill usage will face unprecedented supply chain breaches targeting their AI coding assistants directly. The future of security engineering is not writing more scripts—it is intelligently composing and securing AI‑powered workflows at scale.
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