Root-Cause & Secure-Code Remediation: CVE-2025-29927
Fix CVE-2025-29927 at the source. Read the vulnerable Next.js request pipeline, see how it skips middleware based on the client x-middleware-subrequest header (CWE-285), reject a known-value comparison, derive the skip decision from an internal server-set signal and strip the header at the edge, and verify with audit and vulnscan.
Skills you will practice
- Secure software design
- trust boundaries; Auth bypass
- root cause and remediation; Secure architecture and defense in depth
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.
The scenario
Triage upgraded Next.js; IR handled the breach. You are the security engineer who has to fix the skip logic and harden the edge. Start at the source.
What you will do
- Understand the root cause4 steps
Open the source · Read the root-cause note · Read the vulnerable pipeline · What is the sink?
- Audit and reject the weak fix4 steps
Audit the vulnerable file · Read the proposed fix · Audit the weak fix · Why is the value check insufficient?
- Apply the fix and harden the edge8 steps
Read the correct fix · Audit the correct fix · What makes it safe? · Deploy the fix · …
- Reason and document4 steps
Verify the deployed pipeline · Two layers · Write the PR note · The principle
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.