polkit pwnkit (CVE-2021-4034) → instant root

§ Context

Assumed environment: foothold on a Linux host. polkit / policykit-1 not patched (Ubuntu < 18.04.6, CentOS 7.9, etc.). Compilers or a precompiled binary available.

§ Steps

1. 01
   Low-priv shellInitial Access

   T1078— Valid Accounts
2. 02
   Compile / drop exploitExecution

   T1059— Command and Scripting Interpreter
3. 03
   Check pkexec / polkit versionDiscovery

   T1518— Software Discovery
4. 04
   Run pwnkit → root shellPrivilege Escalation

   L-POLKIT-PWNKIT— polkit pwnkit (CVE-2021-4034)
5. 05
   SSH key + cronPersistence

   L-SSH-AUTHKEYS— SSH authorized_keys Backdoor

§ References

• T1078Valid Accounts
• T1059Command and Scripting Interpreter
• T1518Software Discovery

§ Frequently asked

What is the "polkit pwnkit (CVE-2021-4034) → instant root" attack path?

Pre-2022 pkexec has a heap-overflow exploitable with no special permissions. Compile / drop the exploit, run as low-priv user, gain root. It chains 5 steps drawn from real-world offensive-security techniques.

What starting position does this attack require?

The first step is Low-priv shell (T1078) — a initial access primitive. Assumed environment: foothold on a Linux host.

What is the final impact of this kill-chain?

The final step lands on SSH key + cron (L-SSH-AUTHKEYS), which falls under Persistence. From here, an operator typically pivots into post-exploitation or maintains persistence.

How can defenders detect or prevent this attack?

Detection and prevention vary per step. Refer to each linked MITRE ATT&CK entry under "References" — every technique on that page lists defensive controls, detection telemetry, and known threat-actor usage.

§ Related dossiers

• Shared techniques3

  Exposed UART → root shell → firmware extraction

  Open the IoT device, locate TX/RX/GND pads, attach a USB-UART, get an unauthenticated root prompt, dump firmware for offline analysis + 0-day hunting.

• Shared techniques3

  AlwaysInstallElevated → SYSTEM via MSI

  Both HKCU and HKLM AlwaysInstallElevated policies set to 1 — any user-installed MSI runs as SYSTEM. Drop a malicious MSI and install it.

• Shared techniques3

  SUID binary → root via GTFOBins

  Find an unusual SUID binary (find / nmap / vim / awk / less), check GTFOBins for the privilege-escalation primitive, spawn a root shell.

• Shared techniques2

  io_uring UAF → modprobe_path overwrite → root

  Use an io_uring UAF to land arbitrary kernel write, repoint /proc/sys/kernel/modprobe to an attacker binary, then trigger a kernel auto-modprobe — runs the binary as root.

• Shared techniques2

  nf_tables UAF → kernel R/W → root

  CVE-2024-1086-class nf_tables UAF reachable from a user namespace. Win the race with userfaultfd to land an attacker object in the freed slot, build a kernel R/W primitive, overwrite the current task's cred struct.

• Shared techniques2

  Process doppelgänging → spawn signed image with attacker bytes

  Use NTFS transactional file APIs to overlay an attacker image during process creation. The final mapped process differs from the on-disk file — AV sees only the legit signed image at scan time.