VPN & Privilege Escalation — Case Study

Assessor: inkedqt • Version: 1.0

This is a generalized, platform-agnostic case study derived from a lab scenario. It contains no hostnames, IPs, or flags.

Executive Summary

An internet-facing VPN service exposed IKE Aggressive Mode, enabling capture and offline cracking of the pre-shared key (PSK). Using the recovered PSK to authenticate, an attacker obtained a foothold and discovered a sudo host option path to root on the target host. The combination yields full system compromise, credential exposure, and potential lateral movement into internal networks.

Overall Risk: High
Key Recommendations: Disable Aggressive Mode or use certificates/MFA; enforce strong PSKs with rotation; update and restrict sudo to explicit commands; centralize logging/alerting on VPN and sudo events.

Scope & Assumptions

• In scope: Internet-exposed VPN/IKE service; reachable host after VPN access; host-level privilege escalation.
• Out of scope: DoS, third-party providers, physical access.
• Constraints: Black-box approach with standard wordlists and public tooling; minimal-impact verification of PoCs.

Methodology (Condensed)

1. Recon: UDP/500 (ISAKMP/IKE) & UDP/4500 (NAT-T) identified.
2. IKE Testing: Attempted Main vs Aggressive Mode; captured Aggressive Mode exchange for offline cracking.
3. Foothold: Validated recovered PSK/credentials; established host access.
4. Privilege Escalation: Enumerated sudo behavior; verified -h <hostname> path to root shell.
5. Validation: Read-only checks where feasible; gathered evidence and remediations.

Findings

FN‑01: IKE Aggressive Mode with Crackable PSK — High

Category: Weak cryptographic configuration (CWE‑326)
Description: The VPN gateway supports Aggressive Mode, which leaks enough data to allow offline PSK cracking. With common wordlists, the PSK was recovered and accepted by the service.
Impact: External attackers can obtain VPN/host access and pivot internally.
Likelihood: High • Severity: High
Evidence (generalized):

ike-scan -A --pskcrack=out.txt <target>
psk-crack -d <wordlist> out.txt -> PSK recovered

Remediation:

• Disable Aggressive Mode; prefer Main Mode with certificate-based authentication and/or MFA.
• Enforce strong, non-dictionary PSKs; implement rotation and account lockouts.
• Monitor IKE probing and failed handshake patterns in SIEM.

FN‑02: Sudo Host Option Allowed Root Shell — High

Category: Privilege management misconfiguration (CWE‑266)
Description: The target host permitted a sudo host option path to spawn an interactive root shell (e.g., sudo -h <hostname> -i) without a tight command allow-list and/or due to a vulnerable build.
Impact: Full privilege escalation to root on the host → credential theft, service manipulation, and staging for lateral movement.
Likelihood: High • Severity: High
Evidence (generalized):

/usr/local/bin/sudo -h <trusted-host> -i  # yielded root shell

Remediation:

• Update sudo to the latest stable version; remove duplicate/custom builds.
• Restrict sudoers to specific commands; disallow interactive shells (!SHELLS), enforce TTY and logging.
• Ship sudo logs to SIEM; alert on unusual options (e.g., -h) and failed sudo attempts.

MITRE ATT&CK (Mapping)

• T1078 — Valid Accounts: Access via recovered PSK/credentials.
• T1548.003 — Abuse Elevation Control Mechanism (Sudo and Sudo Caching): Misuse of sudo options to escalate.

Recommendations (Prioritized)

1. 0–7 days: Disable Aggressive Mode or move to certificate-based auth; rotate PSK and any dependent credentials; patch sudo and lock down sudoers.
2. 8–30 days: Add VPN rate-limiting and lockouts; centralize auth via RADIUS/IdP with MFA; enable sudo audit logs & alerts.
3. 31–90 days: Annual VPN hardening review; baselined config management; periodic red-team checks for privesc vectors.

Retest Plan

After remediation is deployed in a staging/production-like environment, rerun IKE mode validation and sudo misuse tests. Document results as Fixed / Partially Fixed / Not Fixed.

Prepared by inkedqt • https://inksec.io