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testing-jwt-token-security

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Assessing JSON Web Token implementations for cryptographic weaknesses, algorithm confusion attacks, and authorization bypass vulnerabilities during security engagements.

internal/tools/skills/data/web-application-security/testing-jwt-token-security/SKILL.md

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# Testing JWT Token Security

## When to Use

- During authorized penetration tests when the application uses JWT for authentication or authorization
- When assessing API security where JWTs are passed as Bearer tokens or in cookies
- For evaluating SSO implementations that use JWT/JWS/JWE tokens
- When testing OAuth 2.0 or OpenID Connect flows that issue JWTs
- During security audits of microservice architectures using JWT for inter-service authentication

### How to CONFIRM a Hit (avoid false negatives)

- **Positive signal**: a token YOU forged (alg=none, RS256→HS256 confusion, cracked HMAC secret, or kid/jku/x5u abuse) is **ACCEPTED by a protected endpoint** — returns 200 plus privileged data for the impersonated identity. Decoding or editing the token alone is not a finding.
- Confirm by calling a real authz-gated route with the forged token and verifying the restricted resource comes back, not a login page, 401, or 403.
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