thinQtankLABS

Detection Engineering & Incident Response: CVE-2025-29927

Respond to a Next.js middleware-auth-bypass compromise (CVE-2025-29927). Reconstruct the timeline from the access and session logs, see how the x-middleware-subrequest header made middleware skip and exposed /admin, find the backdoor-admin persistence, engineer a detection rule for the bypass header, then contain at the edge, eradicate, upgrade, verify and report.

Intermediate 21 guided steps 6 tasks About 75 minutes Runs in your browser

Skills you will practice

  • Log analysis
  • detection and IR; Incident-handling lifecycle; Authorization bypass and IOCs; Security Operations and access control

Certifications this lab maps to

This lab builds hands-on skills that appear on these certification exams. thinQtank Learning runs instructor-led training camps for each — click one to see upcoming classes.

CompTIA CySA+ CS0-003 Log analysis, detection and IR Training at thinQtank Learning EC-Council Certified Incident Handler E|CIH Incident-handling lifecycle Training at thinQtank Learning EC-Council Certified Ethical Hacker CEH Authorization bypass and IOCs Training at thinQtank Learning ISC2 CISSP CISSP Security Operations and access control Training at thinQtank Learning
Part of these certification lab packages: CySA+ CS0-003 CISSP Certified Ethical Hacker (CEH) CEH Certified Incident Handler (E|CIH) E|CIH GCIH GCIH GCIA GCIA

The scenario

A public Next.js app (CVE-2025-29927 open) served /admin with a 200 to an unauthenticated request carrying the x-middleware-subrequest header, then a new admin user appeared. You are the responder. Classify it.

What you will do

  1. Open and classify the incident4 steps

    Open the incident · Read the alert · Read the ticket · Classify it

  2. Reconstruct the timeline3 steps

    Pull the attacker’s requests · Correlate the session log · What caused the bypass?

  3. Impact and persistence3 steps

    Inspect the new account · What persistence? · Record IOCs

  4. Engineer a detection rule4 steps

    Study the sample · Write a rule · Test and tune · Why not flag x-middleware-*?

  5. Contain, eradicate, verify5 steps

    Contain: strip the header at the edge · Eradicate the rogue account · Upgrade Next.js · Verify the host · …

  6. Report2 steps

    Write the report · Design lesson

How this lab works

A real Linux-style console. Commands run against real files, so hashes, hex dumps and comparisons give real results.

A file browser where you can place evidence into the lab, either the file provided or one of your own.

Reset a single step, a whole task or the entire lab. The environment is rebuilt so you can try again cleanly.

Progress saves after every step. Close the tab and come back later; your files and answers are waiting.