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Security 25 errors

Security & Token Errors

JWT validation, CSRF, OAuth grants, SELinux, SSH host keys and CSP.

Understanding Security errors

Security errors are usually a control working correctly. A rejected JWT, a CSP violation, an SELinux denial or a host key mismatch is the system telling you an invariant was broken, and the right response is to understand the invariant, never to disable the control. Two of these deserve special caution: an SSH host key mismatch can indicate a genuine interception, and JWT algorithm confusion is an active exploitation technique, not a configuration nuisance.

How to debug Security errors

  1. Decode tokens locally and check exp, nbf, iss and aud. Never paste a live token into an online decoder. It is a credential.
  2. Pin the accepted JWT algorithm explicitly on the verifying side. Accepting whatever the token's header claims is the algorithm-confusion vulnerability.
  3. For SELinux, read the actual denial: ausearch -m avc -ts recent | audit2why. Set the correct file context with semanage fcontext rather than running setenforce 0.
  4. For CSP violations, read the browser console message. It names the exact directive and blocked URI. Add the specific source, not a wildcard.
  5. For an SSH host key mismatch, verify the new fingerprint out of band before removing the old key. This warning exists to catch man-in-the-middle attacks.

Tools worth reaching for

  • ausearch / audit2why
  • openssl x509 -noout -text
  • ssh-keygen -lf
  • browser CSP console reports
  • local JWT decoding

All 25 Security errors

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