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offensive-jwt

JWT attack methodology for penetration testers. Covers algorithm confusion (alg:none, RS256→HS256), weak HMAC secret brute force, kid parameter injection (SQLi, path traversal), jku/x5u/jwk header injection, JWKS cache poisoning, JWS/JWE confusion, timing attacks, and mobile JWT storage extraction. Use when testing JWT-based authentication, hunting auth bypass via token manipulation, or evaluating JWT implementation security in web or mobile apps.

66

Quality

78%

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SecuritybySnyk

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tessl review fix ./Skills/auth/offensive-jwt/SKILL.md
SKILL.md
Quality
Evals
Security

Quality

Content

57%Weight 40%Scale 1-5

Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.

The body is a thorough, actionable JWT attack reference with concrete commands and payloads, but it is monolithic and somewhat redundant across sections. It lacks explicit validation checkpoints in its testing workflow and does not use reference files to offload detail.

Suggestions

Add explicit validation/confirmation steps to the Manual Testing workflow (e.g., 'Confirm the modified token is accepted by replaying the request; if rejected, try the next variant') so each technique has a verify-decide loop.

Collapse the redundant 'Quick Reference: Misconfigurations to Check', 'Vulnerability Map', and 'Vulnerabilities' sections into a single list, and drop the JWT-structure/algorithms primer that Claude already knows.

Move the large mobile JWT storage extraction, timing-attack, and automated-tool-reference blocks into one-level-deep reference files (e.g., references/mobile-extraction.md, references/timing-attacks.md) with clear links from SKILL.md.

DimensionReasoningScore

Conciseness

Mostly efficient but padded: the 'Mechanisms' section restates JWT structure and lists a signing-algorithm table Claude already knows, and the 'Quick Reference', 'Vulnerability Map', and 'Vulnerabilities' sections repeat the same misconfigurations. It is not a 2 because the bulk is actionable rather than abstract prose, but it could be tightened.

3 / 5

Actionability

Provides concrete, mostly executable guidance — runnable Python timing-attack snippet, specific `jwt_tool.py` flag commands, adb/idevicebackup2 commands, and copy-paste JWT payloads for each technique. Not a 5 because some manual-testing steps show illustrative JSON header fragments rather than complete runnable commands.

4 / 5

Workflow Clarity

A clear sequence exists ('Hunt: Identifying JWT Usage' then numbered 'Manual Testing Steps' 1–8, then automated testing), but there are no explicit validation checkpoints confirming whether a given bypass or injection actually succeeded — checkpoints are only implicit.

3 / 5

Progressive Disclosure

Well-organized into headed sections, but it is a monolithic ~270-line SKILL.md with no bundle files or references; splittable material (mobile JWT storage extraction, timing-attack code, tool reference, remediation) is inlined rather than offloaded to one-level-deep reference files.

3 / 5

Total

13

/

20

Passed

Description

100%Weight 40%Scale 1-5

Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.

The description is specific, comprehensive, and well-triggered, naming concrete attack techniques and providing an explicit 'Use when' clause with natural keywords. It uses third-person voice and avoids fluff or over-claims.

DimensionReasoningScore

Specificity

Lists multiple concrete attack actions — 'algorithm confusion (alg:none, RS256→HS256)', 'weak HMAC secret brute force', 'kid parameter injection (SQLi, path traversal)', 'jku/x5u/jwk header injection', 'JWKS cache poisoning', 'timing attacks', 'mobile JWT storage extraction' — giving comprehensive coverage rather than vague language.

5 / 5

Completeness

Explicitly answers 'what' (the enumerated attack methodology) and 'when' via the concrete 'Use when testing JWT-based authentication, hunting auth bypass via token manipulation, or evaluating JWT implementation security' trigger clause.

5 / 5

Trigger Term Quality

Includes natural user-facing terms and synonyms — 'JWT', 'JWT-based authentication', 'auth bypass', 'token manipulation', 'web or mobile apps' — covering the phrases a tester would actually say.

5 / 5

Distinctiveness Conflict Risk

Occupies a clear niche (JWT offensive testing) with distinct, specific triggers; minimal overlap risk with other skills.

5 / 5

Total

20

/

20

Passed

Validation

100%

Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.

Validation16 / 16 Passed

Validation for skill structure

No warnings or errors.

Repository
SnailSploit/Claude-Red
Reviewed

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