In cybersecurity, not all vulnerabilities are created equal. Some are minor annoyances, while others can allow attackers to take complete control of systems across the internet.
To help security teams prioritize risk, vulnerabilities are tracked and rated using the Common Vulnerabilities and Exposures (CVE) system and the Common Vulnerability Scoring System (CVSS). When a vulnerability receives the maximum CVSS score of 10.0, it signals the most severe level of risk.
But what does that score really mean—and what kinds of vulnerabilities earn it?
What Is a CVE?
A CVE (Common Vulnerabilities and Exposures) identifier is a standardized name assigned to a publicly disclosed security flaw. Each CVE has a unique ID such as CVE-2021-44228, allowing researchers, vendors, and defenders to reference the same vulnerability consistently across tools, advisories, and databases. The CVE system is maintained by MITRE and serves as a global catalog of known security issues affecting software and hardware products.
However, a CVE ID alone doesn’t tell you how dangerous the vulnerability is. That’s where CVSS comes in.
What Is a CVSS Score?
The Common Vulnerability Scoring System (CVSS) is a framework used to measure the severity of vulnerabilities on a scale from 0 to 10, with 10 representing the most critical possible risk.
Security teams use CVSS scores to help determine which vulnerabilities require immediate attention.
Scores are grouped into severity ranges; a 10.0 score typically means the vulnerability:
- Can be exploited remotely
- Requires no authentication
- Has low complexity
- Allows complete compromise of confidentiality, integrity, and availability
In other words: attackers can easily exploit it and potentially take over affected systems.
How CVSS Scores Are Calculated
CVSS scores are derived from several technical metrics that describe how a vulnerability behaves. The most important are part of the Base metrics group, which measures the intrinsic characteristics of the flaw (the other two groups are Temporal and Environmental).
Key scoring factors include:
- Attack Vector
- Whether the vulnerability can be exploited remotely over the network or requires local access.
- Attack Complexity
- How difficult exploitation is. Simple attacks increase the score.
- Privileges Required
- Whether the attacker needs credentials before exploiting the vulnerability.
- User Interaction
- If exploitation requires a user action (like opening a file).
- Impact Metrics
- Confidentiality impact – exposure of sensitive data
- Integrity impact – ability to modify data
- Availability impact – ability to disrupt systems
When all these factors align in the worst possible way, the vulnerability receives the maximum CVSS score of 10.0.
10 Vulnerabilities That Earned a Perfect CVSS Score
Here are ten notable vulnerabilities from the past decade that received the highest possible severity rating.
- Log4Shell
CVE-2021-44228 https://nvd.nist.gov/vuln/detail/CVE-2021-44228
Perhaps the most infamous vulnerability of the last decade, Log4Shell affected the widely used Apache Log4j logging library. Attackers could trigger remote code execution simply by sending a specially crafted string that was logged by an application. Because Log4j was embedded in countless enterprise systems, the vulnerability created a massive global patching effort. - SIGRed
CVE-2020-1350 https://nvd.nist.gov/vuln/detail/CVE-2020-1350
Known as SIGRed, this vulnerability affected Microsoft Windows DNS servers. It allowed attackers to send specially crafted DNS responses that could trigger remote code execution, potentially enabling worm-like propagation across networks. - Citrix ADC Directory Traversal
CVE-2019-19781 https://nvd.nist.gov/vuln/detail/CVE-2019-19781
This vulnerability in Citrix Application Delivery Controller (ADC) allowed attackers to exploit a directory traversal flaw to execute arbitrary commands on affected systems without authentication. - Cisco IOS XE Web UI
CVE-2023-20198 https://nvd.nist.gov/vuln/detail/CVE-2023-20198
A critical vulnerability in Cisco IOS XE’s web interface allowed attackers to create privileged accounts and take over devices running the software. Because many enterprise network devices expose this interface, the flaw posed significant risk. - XZ Utils Backdoor
CVE-2024-3094 https://nvd.nist.gov/vuln/detail/CVE-2024-3094
One of the most dramatic supply-chain security events in recent memory, this vulnerability involved a malicious backdoor inserted into the widely used XZ compression library. The backdoor targeted Linux systems and could allow attackers to gain remote access through SSH authentication mechanisms. - Cisco ASA XML Packet Processing
CVE-2018-0101 https://nvd.nist.gov/vuln/detail/CVE-2018-0101
A flaw in Cisco Adaptive Security Appliance software allowed attackers to send crafted XML packets to trigger remote code execution on VPN-enabled devices. - F5 BIG-IP iControl REST Authentication Bypass
CVE-2022-1388 https://nvd.nist.gov/vuln/detail/CVE-2022-1388
This vulnerability allowed attackers to bypass authentication on F5 BIG-IP systems and execute arbitrary commands with root privileges, potentially compromising load balancers and application delivery systems. - Spring4Shell
CVE-2022-22965 https://nvd.nist.gov/vuln/detail/CVE-2022-22965
Nicknamed Spring4Shell, this vulnerability affected the widely used Spring Framework for Java applications. Under certain conditions, attackers could exploit it to achieve remote code execution on vulnerable servers. - Cisco BroadWorks SSO Authentication Bypass
CVE-2023-20238 https://nvd.nist.gov/vuln/detail/CVE-2023-20238
A flaw in Cisco BroadWorks authentication allowed attackers to forge credentials and access systems without valid authentication, potentially compromising telecom infrastructure. - XiongMai uc-httpd Buffer Overflow
CVE-2018-10088 https://nvd.nist.gov/vuln/detail/CVE-2018-10088
This vulnerability affected a lightweight web server commonly used in IoT devices. A buffer overflow allowed attackers to execute arbitrary code remotely, exposing large numbers of embedded devices.
Why CVSS 10 Vulnerabilities Matter
A CVSS score of 10 doesn’t necessarily mean a vulnerability will cause widespread attacks, but it does mean it has the potential to do so.
Many of the most disruptive cybersecurity events—from Log4Shell to supply-chain compromises—stem from vulnerabilities that were easy to exploit and widely deployed.
For security teams, the lesson is clear: vulnerabilities with critical scores demand immediate attention. Understanding how CVSS scores work—and what makes a vulnerability truly dangerous—helps organizations prioritize patching, reduce risk, and stay ahead of attackers.