Operating System Vulnerabilities
Security weaknesses at the operating system level including kernel vulnerabilities, privilege escalation paths, system misconfigurations, and exposed services. These vulnerabilities can lead to complete system compromise.
Understanding Operating System Vulnerabilities
Operating system vulnerabilities affect the core software that manages computer hardware and provides services to applications. Because the OS has the highest privileges on a system, OS vulnerabilities can lead to complete system compromise.
Key OS vulnerability categories: • Kernel vulnerabilities — Flaws in the OS core • Privilege escalation — Gaining elevated permissions • Service vulnerabilities — Flaws in OS-provided services • Misconfigurations — Insecure default or manual settings
OS security is critical because compromising the OS gives attackers control over everything running on it.
Why This Matters for the Exam
OS vulnerabilities are fundamental to system security and tested throughout SY0-701. Understanding privilege escalation is especially important—it's how initial access becomes full compromise.
Patching OS vulnerabilities is a core security activity. Knowing why OS patches are critical helps prioritize security efforts.
The exam tests understanding of how OS vulnerabilities differ from application vulnerabilities and appropriate mitigations for each.
Deep Dive
Kernel Vulnerabilities
The kernel is the core of the operating system—vulnerabilities here are extremely serious.
What the Kernel Does:
- •Manages memory
- •Controls processes
- •Handles I/O
- •Enforces security boundaries
- •Provides system calls
Kernel Vulnerability Types:
| Type | Description | Impact |
|---|---|---|
| Buffer overflow | Overflow in kernel code | Root/SYSTEM access |
| Use-after-free | Using freed kernel memory | Code execution |
| Race condition | Timing flaws in kernel | Privilege escalation |
| Null pointer | Dereferencing null in kernel | System crash or exploit |
Kernel Exploitation:
- •Requires local access or remote kernel-level bug
- •Results in highest privilege (ring 0)
- •Can bypass all OS security controls
- •Often enables rootkit installation
Kernel Hardening:
- •Keep kernel updated
- •Enable kernel security features (KASLR, SMEP)
- •Minimize kernel modules
- •Use secure boot
Privilege Escalation
Gaining higher permissions than originally granted.
Privilege Escalation Types:
Vertical Escalation
- •User → Administrator/Root
- •Lower privilege → Higher privilege
- •The classic "become admin" attack
Horizontal Escalation
- •User A → User B (same privilege level)
- •Access another user's data/resources
- •Often overlooked but still serious
Common Escalation Methods:
| Method | Description |
|---|---|
| Kernel exploits | Exploit kernel vulnerability for root |
| SUID/sudo abuse | Exploit setuid binaries or sudo rules |
| Service exploits | Exploit service running as root |
| Credential theft | Find stored passwords or tokens |
| Misconfiguration | Exploit weak permissions |
| DLL hijacking | Load malicious DLL in privileged process |
Windows-Specific Escalation:
- •Token impersonation
- •Unquoted service paths
- •DLL search order hijacking
- •SeImpersonatePrivilege abuse
Linux-Specific Escalation:
- •SUID/SGID binaries
- •Cron job exploitation
- •Path injection
- •Capability abuse
System Service Vulnerabilities
OS services running with elevated privileges.
Vulnerable Service Categories:
- •Remote access (SSH, RDP, Telnet)
- •File sharing (SMB, NFS)
- •Print services
- •Management services
- •Authentication services
Service Vulnerability Examples:
- •EternalBlue (SMB vulnerability)
- •BlueKeep (RDP vulnerability)
- •Heartbleed (OpenSSL)
Service Security:
- •Disable unnecessary services
- •Keep services updated
- •Restrict service access
- •Use service-specific security settings
- •Run services with minimal privileges
OS Misconfigurations
Insecure settings that create vulnerabilities.
Common Misconfigurations:
| Misconfiguration | Risk |
|---|---|
| Weak file permissions | Data exposure, escalation |
| Disabled security features | Reduced protection |
| Unnecessary services enabled | Expanded attack surface |
| Default accounts active | Easy compromise |
| Missing patches | Known vulnerabilities |
| Insecure authentication | Credential attacks |
Configuration Hardening:
- •Follow security benchmarks (CIS)
- •Remove default accounts
- •Apply principle of least privilege
- •Enable security features (firewall, AV)
- •Audit configurations regularly
Unpatched Operating Systems
Systems missing security updates remain vulnerable.
Patch Importance:
- •Fixes known vulnerabilities
- •Closes exploitation windows
- •Required for compliance
- •Reduces attack surface
Patch Challenges:
- •Testing requirements
- •Downtime needed
- •Compatibility concerns
- •Volume of patches
How CompTIA Tests This
Example Analysis
Scenario: An attacker gains access to a Linux server through a web application vulnerability. They now have shell access as the "www-data" user. They discover that a backup script (/usr/local/bin/backup.sh) runs as root via cron and is world-writable.
Analysis - Privilege Escalation:
Attack Path: 1. Initial access as www-data (low-privilege web user) 2. Discover world-writable script that runs as root 3. Modify script to add malicious commands 4. Wait for cron to execute script 5. Malicious commands run as root
Exploitation: ```bash echo "cp /bin/bash /tmp/rootbash && chmod +s /tmp/rootbash" >> /usr/local/bin/backup.sh ``` When cron runs the script as root, it creates a SUID bash shell.
Why This Works: • Misconfiguration: Script writable by non-root users • Dangerous pattern: World-writable script running as root • No privilege separation
Defenses: • Proper file permissions (root-owned, not writable by others) • Use absolute paths in scripts • Validate cron job permissions • Implement least privilege • Regular security audits
Key insight: Privilege escalation often chains small misconfigurations into full compromise.
Key Terms to Know
Common Mistakes to Avoid
Exam Tips
Memory Trick
"KPSM" - OS Vulnerability Categories
- •Kernel vulnerabilities (core OS flaws)
- •Privilege escalation (gain higher access)
- •Service vulnerabilities (running services)
- •Misconfigurations (insecure settings)
- •Escalation Direction:
- •Vertical = Very different privilege (up)
- •Horizontal = Hidden (same level, different user)
- •Linux Escalation Targets: "SSCCP"
- •SUID binaries
- •Sudo misconfig
- •Cron jobs
- •Capabilities
- •Path injection
- •Windows Escalation Targets: "TUDS"
- •Token impersonation
- •Unquoted service paths
- •DLL hijacking
- •Service exploits
Test Your Knowledge
Q1.An attacker with limited user access exploits a kernel vulnerability to gain root access. This is an example of:
Q2.What makes kernel vulnerabilities particularly dangerous compared to application vulnerabilities?
Q3.A Linux system has a cron job running a script as root, but the script is writable by regular users. What type of vulnerability is this?
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