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What Is a Zero-day Attack?

What is a Zero-Day Vulnerability or Exploit?

A zero-day (or 0-day) vulnerability is a security risk in a piece of software that is not publicly known about and the vendor is not aware of. A zero-day exploit is the method an attacker uses to access the vulnerable system. These are severe security threats with high success rates as businesses do not have defenses in place to detect or prevent them.

A zero-day attack is so-called because it occurs before the target is aware that the vulnerability exists. The attacker releases malware before the developer or vendor has had the opportunity to create a patch to fix the vulnerability.

The term "zero day" comes from the world of pirated digital media. A pirated version of a movie, music, or software is referred to as "zero day" when it becomes available at the same time or before the official release. In other words, the pirated version is published zero days after the official version.

How a Zero-Day Exploit Works

A zero-day attack begins with a software developer releasing vulnerable code that is spotted and exploited by a malicious actor. The attack is then either successful, which likely results in the attacker committing identity or information theft, or the developer creates a patch to limit its spread. As soon as a patch has been written and applied, the exploit is no longer referred to as a zero-day exploit.

The timeline of zero-day exploitation has been split into seven separate stages by security researchers Leyla Bilge and Tudor Dumitras from vulnerability introduction to security patch. They are as follows:

Stage 1

Vulnerability introduced: A developer creates software that, without them realizing, contains vulnerable code.

Stage 2

Exploit released: A malicious actor discovers the vulnerability before the developer realizes it exists or before they have been able to fix or patch it. The hacker then writes and deploys an exploit code while the vulnerability is still open.

Stage 3

Vulnerability discovered: The vendor becomes aware of the vulnerability but does not have a patch available.

Stage 4

Vulnerability disclosed: The vendor and/or security researchers announce the vulnerability publicly, which advises users and attackers of its existence.

Stage 5

Antivirus signatures released: If attackers have created zero-day malware targeting the vulnerability, then antivirus vendors can quickly identify its signature and provide protection against it. However, systems may remain exposed if there are other ways of exploiting the vulnerability.

Stage 6

Security patch released: The vendor releases a public fix to close the vulnerability. How long this takes to arrive depends on the complexity and how much of a priority it takes in their development process.

Stage 7

Security patch deployment completed: Releasing a security patch does not provide an instant fix as it can take time for users to deploy it. For this reason, organizations and individual users should switch on automatic software updates and take notice of update notifications.

Systems are vulnerable to attack through the entire process from stages 1 to 7, but a zero-day attack can only occur between stages 2 and 4. Further attacks can occur if the vulnerability remains unprotected. Zero-day attacks are rarely discovered quickly enough to prevent substantial damage. It can typically take days, months, and even years before a developer realizes the vulnerability existed and led to an attack and data breach.

Zero-Day Threat Examples

A zero-day attack can happen to any company at any time, often without them realizing. High-profile examples of zero-day attacks include:

  1. Sony Pictures: Potentially the most famous zero-day attack took down the Sony network and led to the release of its sensitive data on file-sharing sites. The attack, in late 2014, saw the leak of information around upcoming movies, the company’s business plans, and personal email addresses of senior executives.
  2. RSA: Another highly public zero-day attack saw hackers use an unpatched vulnerability in Adobe Flash Player to gain access to the network of security firm RSA in 2011. The attackers sent emails attached with Excel spreadsheets, which contained an embedded Flash file that exploited the zero-day vulnerability, to RSA employees. When employees opened the spreadsheet, it gave the attacker remote control of the user’s computer, which they used to search for and steal data. That information turned out to be related to its SecurID two-factor authentication products that employees use to access sensitive data and devices.
  3. Operation Aurora: In 2009, a zero-day exploit targeted the intellectual property of more than 20 major global organizations, including Adobe Systems, Blackberry, Dow Chemical, Google, Morgan Stanley, and Yahoo. It exploited vulnerabilities in Internet Explorer, various other Windows software versions, and Perforce, which Google used to manage its source code. The attack aimed to gain access to and modify source code repositories at high-tech organizations.

How to Protect Against Zero-Day Attacks

While a zero-day attack, by its very definition, is impossible to patch, there are methods that allow organizations to defend against them.

Vulnerability Scanning

Solutions that scan for vulnerabilities can simulate attacks on software code, review code for errors, and attempt to find new issues that have been introduced in a software update. However, this approach will not detect all zero-day exploits, and scanning alone is not enough. Businesses need to act quickly on the results of a scan and review code to prevent an exploit.

Patch Management

Patch management: Deploying software patches as soon as possible after discovering a software vulnerability can reduce the risk of an attack. However, it cannot prevent an attack if the hacker creates their exploit quicker than the patch is deployed. The longer the patch process takes, the higher the risk of a zero-day attack occurring.

Input Validation

Input validation: Input validation, or data validation, is the proper testing of any input supplied by an application or user to prevent improperly formed data from entering a system. It protects organizations through the vulnerability scanning and patch management process and enables them to respond to new threats in real time. One of the best ways to prevent zero-day attacks is to deploy a web application firewall (WAF) on the network edge to review incoming traffic and filter out malicious inputs that could target security vulnerabilities.

Zero-Day Initiative

The zero-day initiative is a program that rewards security researchers for disclosing vulnerabilities rather than selling them on the black market. Its aim is to create a community of vulnerability researchers who discover software problems before hackers do. In addition, organizations also offer bug bounty programs that compensate individuals for reporting vulnerabilities to them.

How To Reduce Zero-Day Vulnerability

To remain vigilant against the threat of zero-day attacks, businesses must have a strategy in place.

Stay Informed

Being proactive and staying informed on the latest risks in the threat landscape is a vital first step in preventing zero-day attacks. This includes deploying comprehensive security software that will block known and unknown threats. It also includes employees practicing safe and secure online habits and configuring security settings for their browsers and systems. The Fortinet FortiGuard Labs team is committed to discovering new and emerging threats and delivering instant protection to Fortinet solutions before such threats pose a security problem for organizations.

Perform System Updates

Ensuring systems are up to date is crucial to protecting a business from the risk of zero-day attacks. This includes having the latest features installed, removing outdated or defunct features, updating drivers, fixing bugs, and filling potential holes in security.

Use A Next-Generation Firewall

Traditional antivirus software cannot effectively protect businesses from zero-day threats. Instead, businesses need to look for solutions that block unknown zero-day malware. The Fortinet NGFW does this by combining deeper inspection capabilities that identify advanced attacks, malware, and threats. It not only blocks malware but also provides the flexibility to evolve with the threat landscape and keep organizations’ networks secure as new threats emerge.