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exploiting-jwt-algorithm-confusion-attack

95 / 100 · Low risk

Fine to try. Some of what it can do is expected: a security skill usually runs scanners and checks websites.

By mukul975/Anthropic-Cybersecurity-Skills (GitHub) · security · 35,906 stars · scanned at commit 54a7988

Exploits JWT algorithm confusion where the server's verification library trusts the alg named in the token header, by switching RS256 to HS256 (signing with the RSA public key as HMAC secret), setting alg to none, or injecting kid/jku/x5u headers to supply an attacker-controlled key. Use when testing RS256 JWT auth for algorithm downgrade, alg:none bypass, or key-confusion signature forgery.

Works with any agent that supports SKILL.md skills.

What this skill can do

Install

Paste this into your terminal. It downloads exactly the version we scanned, not whatever is newest.

if [ -e ~/.agents/skills/'exploiting-jwt-algorithm-confusion-attack' ] || [ -L ~/.agents/skills/'exploiting-jwt-algorithm-confusion-attack' ]; then echo 'A skill folder named exploiting-jwt-algorithm-confusion-attack already exists — not replacing it' >&2; false; else d=$(mktemp -d) && git clone --quiet --filter=blob:none --no-checkout 'https://github.com/mukul975/Anthropic-Cybersecurity-Skills' "$d" && git -C "$d" checkout --quiet '54a798831d2266a3ca61ce68a7acb80b81160d57' -- 'skills/exploiting-jwt-algorithm-confusion-attack' && mkdir -p ~/.agents/skills && cp -R "$d"/'skills/exploiting-jwt-algorithm-confusion-attack' ~/.agents/skills/'exploiting-jwt-algorithm-confusion-attack' && rm -rf "$d"; fi

Codex reads ~/.agents/skills directly. For Claude Code, Cursor, Copilot, Gemini CLI, Antigravity or OpenCode, also link it. For Claude Code: ln -s ~/.agents/skills/'exploiting-jwt-algorithm-confusion-attack' ~/.claude/skills/'exploiting-jwt-algorithm-confusion-attack' (other agents: ~/.cursor/skills, ~/.copilot/skills, ~/.gemini/skills, ~/.gemini/config/skills, ~/.config/opencode/skills). Or install through the finder skill, which does both.

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