linux-privesc

name

linux-privesc

description

Linux local privilege escalation methodology for authorized pentesting and CTF — turn a foothold shell (often a low-priv/service account like www-data) into root. Use after landing any non-root shell on a Linux host and you need to escalate: enumerate the local attack surface (sudo, SUID/SGID, capabilities, cron/timers, writable files, internal root services, credential reuse, kernel) and exploit the weakest link. Triggers on "privesc", "privilege escalation", "I have a shell now what", "escalate to root", "get root", "I'm www-data", "root this box", "linpeas", "sudo -l", "SUID", "GTFOBins".

Linux local privilege escalation

You have a shell as a non-root user (commonly a service account — www-data, mysql, an app user). Goal: become root. This skill is the enumerate → find the one thing you can influence that runs as root → exploit loop, plus the footguns of driving a half-broken foothold shell.

Scope guardrail

Authorized targets only (CTF box, lab, signed scope). Enumeration maps the local attack surface; the actual escalation is an acting step — surface the vector and the one-liner, and let the operator approve before you fire it (same ethos as the rest of the repo). Reading root.txt proves the privesc; don't go beyond the assessment objective.

First: stabilise the foothold

A webshell or raw reverse shell is not a TTY, and several escalation steps need one.

• Get a PTY before anything interactive (su, sudo, ssh, editors): python3 -c 'import pty; pty.spawn("/bin/bash")' (or script -qc /bin/bash /dev/null). Without it, su fails with "must be run from a terminal" and sudo can't prompt.
• For a durable, shareable shell use the catch skill (./roo catch) — drive it with catch send/capture (run catch enter once to drop from pwncat's local prompt into the remote shell).
• For clean, scriptable command output, driving the webshell (single commands via curl --data-urlencode) is often tidier than scraping a tmux pane.

The enumeration ladder (run top-to-bottom; stop when one pays off)

1. Who am I / quick wins. id; sudo -n true 2>&1; cat /etc/passwd | grep sh$. Note your groups — docker, lxd, disk, adm, sudo/wheel are each a known root path on their own.
2. sudo rights. sudo -l (try with and without the foothold password). Any allowed binary → check GTFOBins for the sudo escape. (ALL) NOPASSWD on anything scriptable is usually instant root.
3. SUID / SGID. find / -perm -4000 -type f 2>/dev/null (and -2000). Diff against a stock list — anything non-standard (custom binary, an interpreter, a GTFOBins entry) is the lead. Stock set (mount, su, sudo, passwd, …) is noise.
4. Capabilities. getcap -r / 2>/dev/null. cap_setuid/cap_dac_read_search on a binary you can run = root or arbitrary file read.
5. Cron & timers. cat /etc/crontab; ls -la /etc/cron.*; systemctl list-timers. A root job that runs a script you can write (or a relative/PATH-resolved binary you can hijack, or a wildcard you can inject) → root.
6. Writable things root trusts. Writable /etc/passwd, /etc/sudoers.d/*, a systemd unit, a script invoked by a root service/cron, or a directory on root's PATH. find / -writable -type f 2>/dev/null (filter to /etc,/opt,/usr/local).
7. Internal services running as root. ss -tlnp — a daemon bound to 127.0.0.1 is often more privileged and less guarded than the public ones (admin panels, job/automation runners, DBs, message queues). If it runs as root and exposes any way to run a command, render a template, or read/write a file, that's your primitive — reach it locally (curl, or ./roo fwd to pull it to the host) and look for a command/exec/file feature, an unauthenticated trigger, or an argument/parameter injected into a shell string (loosely-validated inputs in a config-driven action runner are a classic — break out of the surrounding quoting). A root-owned web server (e.g. php -S 127.0.0.1:PORT -t <dir> running as root) is the same primitive by another name: if any feature writes a file into its docroot — even a "save"/upload that basename-sanitizes the name — drop an executable extension (.php) and request it → RCE as root. A surviving .php is enough; you don't need path traversal or command injection in the filename.
8. Credential reuse — try this before cracking. The fastest "privesc" is a found plaintext password, and a reused cred beats a GPU every time — so the moment you have file read (a shell or RCE), scrape for creds before reaching for hashcat. App config files are the richest source (DB/app creds — e.g. wp-config.php DB_PASSWORD, config*.php, .env, settings.py) — a service/DB password from a config is frequently reused as a login user's system password — plus shell history, backups, /var/mail, world-readable home files, and any DB you can reach. Then spray: su <user> for every local user, and reuse on SSH (a service/DB password reused for a login account is a classic foothold→user hop). Only hand what stays a hash to the hashcat skill (-m 1800 sha512crypt, -m 3200 bcrypt) — even "slow" hashes fall fast if it's a common word, and spray any crack result too.
9. Kernel / distro / installed software. uname -a; cat /etc/os-release; dpkg -l → feed versions to the vuln-research skill (./roo vulns) for a local-exploit CVE. Lowest priority on a maintained box; don't lead with a kernel exploit.

Tooling

• Manual first (the ladder above) — it's fast and quiet, and you learn the box.
• Stage an automated enumerator when manual stalls: drop linpeas.sh onto the target (host it from ./roo shell / ./roo catch upload, or fetch with the box's own curl/wget) and run it. Downloads egress the public internet, not the VPN.
• GTFOBins (gtfobins.github.io) is the lookup for sudo/SUID/capability escapes.

Confirm & hand off

• Root proof: a SUID-root shell (cp /bin/bash /tmp/rootbash; chmod 4755 /tmp/rootbash; /tmp/rootbash -p) or a root reverse shell; then id (euid=0) and cat /root/root.txt.
• Note any artifact you leave (a SUID bash, an added user, a modified file) so the operator can clean up — on a lab box it's wiped at reset, but say so.
• Handoffs: hashcat (crack looted hashes), vuln-research (service/kernel CVEs), catch (stabilise/keep the shell), memforensics (if you loot a memory image), ad (if the box is domain-joined and you find domain creds).