Nuclei is an open-source vulnerability scanning tool from ProjectDiscovery that runs YAML-defined templates against a target list to detect CVEs, misconfigurations, exposed panels, and default credentials at scale. Unlike a manual pentest, Nuclei is built for continuous, repeatable scanning — the same template set runs identically today, tomorrow, and inside a CI/CD pipeline on every deploy. For Indian DevSecOps teams managing dozens or hundreds of assets, Nuclei closes the gap between periodic manual VAPT and the daily drift of new subdomains, new services, and newly disclosed CVEs that manual testing cycles simply cannot keep pace with. It complements manual penetration testing; it does not replace it.
What Nuclei Vulnerability Scanning Actually Does
Nuclei vulnerability scanning takes a list of targets (URLs, IPs, or hostnames) and a set of YAML templates, then sends each template's defined requests to each target and evaluates the response against a matcher — a string, regex, status code, or word that confirms the finding. Because templates are plain YAML rather than compiled code, the community-maintained nuclei-templates repository has grown to thousands of checks contributed by researchers worldwide, updated continuously as new CVEs and exposures are disclosed.
The engine itself is written in Go and designed for concurrency — it can fan out requests across thousands of hosts in parallel, rate-limited to avoid overwhelming target infrastructure. That combination of a fast engine and a crowdsourced, constantly-updated template library is what makes Nuclei suitable for continuous scanning rather than a one-off tool run.
Template Categories: What Gets Detected
Templates in the public repository are organised into categories, and understanding the split matters when you decide what to enable in a production scanning pipeline.
| Category | What it finds | Typical risk if triggered |
|---|---|---|
| CVEs | Known, versioned vulnerabilities in software and frameworks | Direct exploit path, often with public PoC |
| Misconfigurations | Default installs, exposed debug endpoints, verbose error pages | Information disclosure, privilege escalation |
| Exposures | API keys, .git directories, backup files, config files left public | Credential theft, source code leak |
| Default logins | Unchanged vendor default credentials on admin panels | Full admin takeover |
| Takeovers | Dangling DNS records pointing to unclaimed cloud resources | Subdomain hijack |
| Network | Open ports, exposed services, protocol-level misconfigurations | Lateral movement entry point |
-severity critical,high and relevant tags is the standard way to keep a CI scan fast and focused rather than running the entire template set on every build.Running Nuclei at Scale Against Your Own Asset List
The core DevSecOps use case is not "scan one target once" — it's "scan every asset your organisation owns, continuously." That starts with an accurate, current inventory. Nuclei accepts a plain text file of URLs or hosts via -list, which is typically fed from asset discovery tooling (subdomain enumeration, cloud asset inventories, or an internal CMDB).
nuclei -list targets.txt -t cves/ -t exposures/ -severity critical,high -rate-limit 150 -o results.jsonRunning at scale introduces operational constraints that a single ad-hoc scan doesn't: rate limiting so scans don't degrade production services, timeout tuning for slow or geographically distant assets, and scheduling so the full template set runs on a cadence (daily incremental, weekly full) rather than as one massive blocking job. Output in structured JSON is what makes the results consumable by downstream tooling — ticketing systems, SIEMs, or a triage dashboard — instead of a scroll of terminal text nobody reads twice.
Know your vulnerabilities before attackers do
Run a free VAPT scan — takes 5 minutes, no signup required.
Book Your Free ScanWriting Custom Templates
Public templates cover known, disclosed issues. They will never cover your organisation's internal APIs, custom authentication flows, or business-logic-specific misconfigurations — for that, teams write custom templates. A Nuclei template is a YAML file with an id, info block (name, author, severity, tags), and one or more request blocks defining the HTTP method, path, headers, and body, paired with a matchers block that defines success conditions.
id: internal-debug-endpoint
info:
name: Internal Debug Endpoint Exposed
severity: high
tags: exposure,custom
http:
- method: GET
path:
- "{{BaseURL}}/debug/vars"
matchers:
- type: status
status:
- 200Custom templates let a security team codify institutional knowledge — "this internal endpoint should never be reachable from outside the VPC" — into a check that runs automatically on every scan, rather than relying on someone remembering to test it manually each quarter.
CI/CD Integration
The highest-leverage place to run Nuclei is inside the deployment pipeline itself, not as a separate weekly job disconnected from the release cycle. A typical pattern: on every merge to a staging or pre-production branch, a pipeline stage runs Nuclei against the newly deployed environment with a curated, fast template subset (critical and high severity only, tagged for the relevant stack — say, nginx, wordpress, or nodejs), and fails the build or opens a ticket if a match is found.
This shifts vulnerability detection left — a misconfigured header or an exposed .env file is caught before it reaches production, not three months later during the next scheduled VAPT engagement. It also builds an audit trail: every deploy has an associated scan record, which is valuable evidence during compliance reviews.
Triage and False-Positive Management
Automated scanning at scale produces noise, and unmanaged noise is how a security team stops trusting — and eventually stops reading — its own scan output. Every finding needs a triage step before it becomes an action item: confirm the match is genuine (not a matcher firing on a benign response), assess real exploitability in context (an exposed .git directory on an internal-only staging box is lower urgency than the same finding on a public production domain), and assign ownership.
A practical triage workflow: critical and high severity findings route to an on-call security or dev channel for same-day review; medium and low severity findings batch into a weekly review; confirmed false positives get suppressed at the template or target level so they don't regenerate noise on every subsequent scan run. Nuclei supports exclusion via -exclude-id and target-specific configuration files precisely so that a known, accepted finding doesn't keep re-triggering alerts.
Where Nuclei Fits — and Where It Doesn't
Nuclei is signature and pattern-based. It matches requests and responses against known conditions — it does not understand your application's business logic, cannot chain multiple low-severity findings into a novel exploit path the way a skilled human tester can, and will not find a logic flaw like a broken authorisation check on an endpoint that returns a "normal-looking" 200 response. That's the boundary between continuous automated scanning and manual VAPT: automation catches the volume of known, pattern-matchable issues fast and repeatedly; manual testing finds the business-logic and chained vulnerabilities that require human judgment and context.
The two are not competing approaches — they're sequential. Continuous Nuclei scanning inside CI/CD keeps the baseline clean between engagements, and periodic manual VAPT — ideally delivered with a CERT-In empanelled partner for regulated or compliance-driven engagements — goes deeper into logic and chained attack paths that no template set can enumerate. Bachao.AI, built by Dhisattva AI Pvt Ltd, is built around that same layered model: automated, continuous checks running alongside structured manual assessment, rather than treating either as sufficient on its own.
Getting Started Without Overcomplicating It
Teams new to Nuclei often try to run the entire template repository against every asset on day one, which produces an unmanageable flood of findings and burns out whoever is triaging them. Start narrower: run critical and high severity CVE and exposure templates against your production asset list first, build a triage process that actually clears the queue, then expand template coverage and add the CI/CD gate once the workflow is proven. Scanning that generates findings nobody reviews accomplishes nothing.
Whether you run Nuclei in-house or want a structured assessment that combines continuous automated scanning with expert manual review, a free VAPT scan is the fastest way to see where your current asset list actually stands. For teams building out a broader DevSecOps security programme, the Bachao.AI blog covers the rest of the toolchain — from network reconnaissance to compliance mapping — in the same practical, no-fluff format.