OpenVAS vs Nessus: which vulnerability scanner fits your team?

OpenVAS and Nessus are the two names that come up first when a small security team or MSP picks a network vulnerability scanner. They share a history: OpenVAS began in 2005 as an open-source fork of Nessus, after Nessus moved to a closed licence. Today Nessus is a commercial product from Tenable, and OpenVAS is the scanning engine inside Greenbone's vulnerability management software, available free as the Greenbone Community Edition and in paid Greenbone products.

This comparison is written from the point of view of someone who has to read and report on the output of both. We do not sell either scanner.

At a glance

Cost

OpenVAS is free to download and run, with no limit on the number of targets. The real cost is time: someone has to install it, keep the feed and components updated, and tune scan configurations. The free Community Feed also covers fewer checks than Greenbone's paid Enterprise feed, particularly for some enterprise products.

Nessus Essentials is free but capped at 16 IP addresses, which suits a lab or a very small office. Nessus Professional is priced per year per scanner with unlimited IPs, and is the usual choice for consultants and MSPs who want a commercial tool without buying a full platform.

Coverage and accuracy

Both scanners detect the common things well: missing operating system patches, out-of-date server software, weak TLS settings, exposed services and end-of-life systems. Tenable's plugin library is larger and new checks often arrive quickly after a major CVE is published. Greenbone's feed is solid for mainstream software, and its results carry a Quality of Detection value that tells you how much to trust each one.

For either tool, the single biggest accuracy factor is authentication. An unauthenticated scan sees only what a service shows over the network; a credentialed scan can read installed package versions and settings. See credentialed vs non-credentialed scans.

Reading the results

This is where daily use differs most. Nessus groups output by plugin, with clear synopsis, description and solution fields, and its .nessus export is well structured. Our guide on how to read a Nessus scan report walks through it.

OpenVAS reports are more raw. Results are tied to NVT OIDs, and many results carry no CVE reference at all, which makes it harder to look up exploitation data. Our guide to why OpenVAS reports show missing CVEs explains why and how to handle it. Expect to spend more time filtering low-confidence and informational results.

Neither scanner checks the CISA KEV catalog or EPSS for you in its default report, so both lists still need ranking by real-world risk. See CVSS vs EPSS vs CISA KEV.

Which should you choose?

Plenty of teams run both: Nessus for client work and OpenVAS as a second opinion or for internal segments. That is a sensible pattern, as long as results from both end up in one ranked list rather than two separate reports.

Turning either export into a report

Whichever scanner you choose, the built-in reports are long and technical, and clients rarely read them. We built Varaxon Scan Hub to read both: upload a .nessus file or an OpenVAS XML or CSV export and it ranks every finding using CISA KEV, EPSS and CVSS, maps OpenVAS checks to CVEs where Greenbone has listed them, and writes an evidence-led report your client can follow. It also compares each scan with the previous one, so you can show what was fixed. See the Nessus and OpenVAS pages, or check an export free before you sign up.

Common questions