Zero-Day Exploit
Zero-Day Exploit
One-liner: An exploit targeting a vulnerability that is unknown to the vendor, meaning no patch exists at the time of attack.
π― What Is It?
A Zero-Day Exploit leverages a security vulnerability that has not yet been discovered or patched by the software vendor. The term "zero-day" refers to the fact that developers have had zero days to fix the issue. These exploits are part of the Exploitation stage of the Cyber Kill Chain and are highly valuable in the threat landscape.
π¬ How It Works
Timeline of a Zero-Day
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β Vulnerability Vulnerability Patch Patch β
β Introduced Discovered Developed Deployed β
β β β β β β
β βΌ βΌ βΌ βΌ β
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β β β β β β
β βββββ Zero-Day ββββΊβββββ Patch Gap βββΊβ β β
β β Window β β β β
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Terminology
| Term | Definition |
|---|---|
| Zero-Day Vulnerability | The unknown flaw itself |
| Zero-Day Exploit | Code that exploits the vulnerability |
| Zero-Day Attack | Use of the exploit against real targets |
| N-Day Exploit | Exploit for known vulnerability (patch exists) |
π Why They Matter
- No Defense: Traditional signature-based detection fails
- High Value: Sold on black market for $10Kβ$2.5M+
- APT Favorite: Used by nation-states and advanced groups
- Low Detection: Difficult to identify without behavioral analysis
Zero-Day Market
| Buyer Type | Price Range | Motivation |
|---|---|---|
| Vendors (Bug Bounty) | $500 - $150K | Fix vulnerabilities |
| Governments | $50K - $2.5M+ | Offensive operations |
| Black Market | $10K - $500K+ | Cybercrime, APT |
π‘οΈ Detection & Prevention
How to Detect
- Behavioral analysis - Detect anomalous behavior, not signatures
- EDR - Monitor for suspicious process chains
- Sandboxing - Analyze suspicious files in isolated environments
- Threat intelligence - Correlate with known threat actor TTPs
- Honeypots - Detect exploitation attempts in decoy systems
How to Prevent / Mitigate
- Defense in depth - Multiple security layers
- Application allowlisting - Only approved software runs
- Least privilege - Limit damage from successful exploits
- Network segmentation - Contain lateral movement
- Virtual patching - WAF/IPS rules to block exploitation
- Rapid patching - Minimize window for N-day attacks
π€ Interview Angles
Common Questions
- "What is a zero-day and how does it differ from a known vulnerability?"
- "How would you protect against zero-day attacks?"
- "Why are zero-days valuable to threat actors?"
STAR Story
Situation: Log4Shell zero-day (CVE-2021-44228) was publicly disclosed.
Task: Protect the organization before an official patch was available.
Action: Immediately applied virtual patching via WAF rules, disabled JNDI lookups where possible, conducted asset inventory to identify vulnerable systems, and monitored for exploitation attempts.
Result: No successful exploitation occurred despite active targeting. Formal patches applied within 72 hours of release.
β Best Practices
- Assume breachβfocus on detection and response, not just prevention
- Participate in bug bounty programs (reduce your own zero-day exposure)
- Implement robust logging for forensic capability
- Subscribe to threat intelligence feeds
- Practice rapid response through tabletop exercises
π Related Concepts
- Cyber Kill Chain
- Exploit
- Vulnerability
- Endpoint detection and response (EDR)
- Intrusion Prevention System (IPS)
π References
- MITRE ATT&CK - Exploitation of Vulnerability
- Zero Day Initiative (ZDI)