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26. Privilege Escalation

26.3 Common Escalation Paths

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sudo misconfiguration. If sudo -l shows you can run an editor, interpreter or shell as root, you can usually get a root shell. The site GTFOBins documents how each binary can be misused.

sudo -l                       # e.g. "(root) NOPASSWD: /usr/bin/find"
sudo find . -exec /bin/sh \; -quit   # abuse find to spawn a root shell (lab example)

SUID binaries. A file with the SUID bit runs with its owner's rights. A misconfigured or vulnerable SUID root binary can give a root shell (check each one on GTFOBins).

find / -perm -4000 -type f 2>/dev/null
# example: an SUID 'nmap' (old interactive mode) or 'cp', 'vim', 'bash' can lead to root

Writable cron job / script. If root runs a script on a schedule and you can edit that script, your code runs as root.

cat /etc/crontab
ls -la /path/to/script/root/runs.sh    # if you can write it, add a reverse shell line

Kernel exploits. A very old kernel may have a local exploit (for example the classic "Dirty COW"). Match uname -r to a known exploit with searchsploit – but kernel exploits can crash the box, so try safer paths first.

Kernel exploits can crash the system

Kernel exploits are the loudest and riskiest option – they can freeze the machine. That is why you take a snapshot first and prefer sudo/SUID/cron paths. In a real job these run only with explicit permission.

Ravindra Bagale's Tip

GTFOBins (gtfobins.github.io) is the "cheat sheet" of privilege escalation – it is where you check which binary can give root. But don't just memorise it; first understand what the command does. "What is SUID?" is a question that almost always comes up in interviews.

Lab

On Metasploitable 2, pick one SUID binary from your list, look it up on GTFOBins, and get a root shell using the documented method. Confirm with id that you are now uid=0(root). Restore the snapshot afterwards.

Extended teaching notes

Why this lesson matters

Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.

Apply the fix across stacks

Same class of bug, same idea in every language.

Java / Spring Boot

Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.

ASP.NET Core

EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.

Node.js / Express

helmet, parameterised SQL, npm audit, avoid eval and shell concat.

Python / Django / Flask / FastAPI

ORM, autoescape, pip-audit, Bandit; never shell=True with user input.

PHP / Laravel

PDO/Eloquent, Blade escaping, composer audit.

Go / Ruby

database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, security headers, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

Private networks, auth on, least-privilege users, no 0.0.0.0/0.

AWS / Azure / GCP

Roles not long-lived keys, private data stores, cloud audit logs on.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.