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ClaudSkills / Security / identity-access

Defend Jwt

Category: Security  ·  Sub-category: identity-access  ·  Last updated:
Defensive methodology against JSON Web Token (JWT) forgery and verification bypass: the alg:none downgrade, RS256-to-HS256 key confusion, unverified signatures, and missing claim checks that let an attacker mint a token your app will trust (MITRE ATT&CK T1606 Forge Web Credentials, then T1550.001 Use Alternate Authentication Material: Application Access Token). Signals live in application and API-gateway logs, WAF logs, and auth-service logs: the decoded JWT header alg and kid, the iss/aud/exp claims, and signature-verification failures. This skill gives the defender view of each bypass, the exact fields to log and alert on, a hypothesis-driven hunt, and library and key-management hardening mapped to ISO 27001:2022 and NIST CSF 2.0. Use when hardening JWT or bearer-token validation, reviewing a JWT auth flow, hunting for alg:none or key-confusion forgery, triaging a spike in JWT signature failures, or deciding how to rotate signing keys.
Security AStatic scan found no risk patternsHow grading works ›

What this skill does

Defend Jwt is a community-contributed Claude Code skill in the identity-access sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/defend-jwt/ and loads when your prompt matches the skill's trigger.

When to invoke it: Use when hardening JWT or bearer-token validation, reviewing a JWT auth flow, hunting for alg:none or key-confusion forgery, triaging a spike in JWT signature failures, or deciding how to rotate signing keys.

Who uses this skill

The Defend Jwt Claude Code skill is built for security engineers, penetration testers, DevSecOps practitioners, and development teams hardening codebases and infrastructure. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 211,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).

How to install

Free

Manual install (2 steps)

mkdir -p ~/.claude/skills/defend-jwt
curl -L https://claudskills.com/skills/defend-jwt/SKILL.md \
  -o ~/.claude/skills/defend-jwt/SKILL.md

Or just download SKILL.md directly and drop it into ~/.claude/skills/defend-jwt/. Claude Code auto-discovers it on next session.

Skills live at ~/.claude/skills/defend-jwt/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\defend-jwt\SKILL.md on Windows. See the full install guide for step-by-step instructions.

Telegram

📱 Install from your phone or desktop Telegram

Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →

Pro

One-click install via the desktop app

The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.

Pro

For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.

See pricing → Download desktop app

Frequently asked questions

How do I install the Defend Jwt Claude Code skill?
Install via the ClaudSkills desktop app (one click) or copy SKILL.md from the source repository to ~/.claude/skills/defend-jwt/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.
What does the Defend Jwt skill do?
Defensive methodology against JSON Web Token (JWT) forgery and verification bypass: the alg:none downgrade, RS256-to-HS256 key confusion, unverified signatures, and missing claim checks that let an attacker mint a token your app will trust (MITRE ATT&CK T1606 Forge Web Credentials, then T1550.001 Use Alternate Authentication Material: Application Access Token). Signals live in application and API-gateway logs, WAF logs, and auth-service logs: the decoded JWT header alg and kid, the iss/aud/exp claims, and signature-verification failures. This skill gives the defender view of each bypass, the exact fields to log and alert on, a hypothesis-driven hunt, and library and key-management hardening mapped to ISO 27001:2022 and NIST CSF 2.0. Use when hardening JWT or bearer-token validation, reviewing a JWT auth flow, hunting for alg:none or key-confusion forgery, triaging a spike in JWT signature failures, or deciding how to rotate signing keys.
Is this skill free to install?
Yes. ClaudSkills is an open registry — every skill keeps its source repository's license, and manual install via copy is free. ClaudSkills Pro ($9/mo, $79/yr, or $149 one-time) adds one-click install via the desktop app and a multi-signal Quality Score.
When should I use the Defend Jwt skill?
Use Defend Jwt when your Claude Code task falls under the Security category — specifically in the identity access area. Claude Code auto-discovers installed skills and invokes the right one based on the task description, so you can also ask Claude directly (e.g. "use Defend Jwt" or describe the task and let Claude pick). Browse related skills at /category/security/.
What is a Claude Code skill and how does the Defend Jwt skill fit in?
A Claude Code skill is a SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Defend Jwt is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Security category. Learn more at /learn/what-is-a-claude-skill/.

Attribution & license

Cite this skill

If you reference this skill in a blog post, paper, or documentation, you can cite it as:

APA
umbrasec-labs. (2026). Defend Jwt [Claude Code skill]. ClaudSkills. https://claudskills.com/skills/defend-jwt/
BibTeX
@misc{defend-jwt-2026,
  author    = {umbrasec-labs},
  title     = {Defend Jwt [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/defend-jwt/}
}

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Security scan

Grade A · scanned 2026-10-25 — free static scan against the OWASP Agentic Skills Top 10.

No risk patterns were found in any of the ten OWASP-aligned categories. How grading works ›

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More Security skills

Browse all Security skills in the ClaudSkills registry, or explore these other picks from the same category:

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