Are CVSS Scores Reliable? The Hidden Flaw in Vulnerability Management
For security teams everywhere, the Common Vulnerability Scoring System (CVSS) is a cornerstone of daily operations. It provides a standardized numerical score to rate the severity of software vulnerabilities, helping organizations prioritize which fires to put out first. But what if this fundamental tool has a critical flaw?
New analysis reveals that the way these scores are commonly calculated and presented is often incomplete, potentially misleading security teams and leaving organizations exposed to significant risk. The problem lies not in the CVSS framework itself, but in its partial implementation.
Understanding the Three Pillars of CVSS
The CVSS framework is designed to be dynamic, consisting of three core metric groups:
- Base Score: This is the number everyone knows. It rates the intrinsic severity of a vulnerability based on static qualities like attack vector, complexity, and impact on confidentiality, integrity, and availability.
- Temporal Score: This metric is designed to modify the Base Score over time. It considers real-world, evolving factors like the availability of an official patch, the existence of a public proof-of-concept (PoC) exploit, or confirmation that the vulnerability is being actively used in attacks.
- Environmental Score: This allows an organization to further tailor the score based on its specific environment, such as the importance of the affected asset or the presence of mitigating controls.
The Temporal Score is arguably the most critical for real-world prioritization. A vulnerability with a high Base Score but no known exploit is far less of an immediate threat than a medium-rated vulnerability that ransomware gangs are actively using. The Temporal Score is meant to provide exactly this context.
The Critical Missing Piece
The central issue highlighted by recent security research is staggering: the vast majority of vulnerabilities are never updated with a Temporal Score. An in-depth study found that over 90% of all CVEs published in the National Vulnerability Database (NVD) only have a Base Score.
This means that for nine out of ten vulnerabilities, the score remains static. It never evolves to reflect the changing threat landscape. A CVE published with a score of 7.5 will likely still show a 7.5 years later, even if a simple, weaponized exploit for it has been circulating on the dark web for months.
This gap can lead to a false sense of security, where teams focus on high-but-unexploitable flaws while missing lower-scored but actively targeted vulnerabilities. This inefficient allocation of resources means that critical patches might be delayed while teams work on issues that pose little to no immediate danger.
The Real-World Impact of Incomplete Scores
When security teams rely solely on the Base Score for patching priority, they are operating with incomplete intelligence. This can lead to several dangerous outcomes:
- Alert Fatigue: IT and security teams are overwhelmed with a long list of “critical” and “high” severity vulnerabilities, making it impossible to address them all. Without context on which ones are actually being exploited, they struggle to know where to begin.
- Misallocated Resources: Countless hours are spent testing and deploying patches for vulnerabilities that attackers are not using, while actively exploited ones remain unpatched.
- Increased Risk Exposure: The most dangerous vulnerabilities are those with known exploits. By failing to prioritize them, organizations leave their most critical systems vulnerable to attack.
How to Build a Smarter Vulnerability Management Strategy
Relying on the CVSS Base Score alone is no longer a viable strategy. To effectively reduce risk, organizations must adopt a more intelligence-driven approach to vulnerability prioritization. Here are actionable steps to take today:
Look Beyond the Base Score
Treat the CVSS Base Score as a starting point, not the final word. Understand that it represents the potential severity of a flaw in a vacuum, not its current risk to your organization.Prioritize Known Exploited Vulnerabilities
The most valuable piece of information you can have is whether a vulnerability is being used in the wild. Make CISA’s Known Exploited Vulnerabilities (KEV) Catalog your primary source for prioritization. If a vulnerability appears on this list, it represents a confirmed, active threat and should be patched immediately, regardless of its CVSS score.Leverage Real-Time Threat Intelligence
Incorporate threat intelligence feeds that monitor for the release of PoC exploit code, chatter on hacker forums, and mentions in threat actor playbooks. The existence of a functional public exploit dramatically increases the likelihood of an attack and should elevate a vulnerability’s priority.Factor in Your Unique Environment
Always consider the context of your own systems. A vulnerability in an internet-facing, mission-critical server is infinitely more important than the same vulnerability on an isolated, internal workstation. Evaluate which assets are most valuable and most exposed to determine your true risk.
In today’s complex threat landscape, a static, one-size-fits-all number is not enough. By moving beyond a simple reliance on the CVSS Base Score and embracing a dynamic, intelligence-led approach, your organization can focus its resources on fixing the flaws that truly matter and build a more resilient security posture.
Source: https://datacenternews.asia/story/study-finds-cve-security-scores-flawed-with-third-unsubstantiated
