Nuclei is based on the concepts of
YAML based template files that define how the requests will be sent and processed. This allows easy extensibility capabilities to nuclei.
The templates are written in
YAML which specifies a simple human readable format to quickly define the execution process.
Guide to write your own nuclei template -
Each template has a unique ID which is used during output writing to specify the template name for an output line.
The template file ends with YAML extension. The template files can be created any text editor of your choice.
ID must not contain spaces. This is done to allow easier output parsing.
Next important piece of information about a template is the info block. Info block provides name, author, severity, description, reference and tags. It also contain severity field which indicates the severity of the template, info block also supports dynamic fields, so one can define N number of
key: value blocks to provide more useful information about the template. reference is another popular tag to define external reference links for the template.
Another useful tag to always add in
info block is tags. This allows you to set some custom tags to a template, depending on the purpose like
rce etc. This allows nuclei to identify templates with your input tags and only run them.
Example of an info block -
info: name: Git Config File Detection Template author: Ice3man severity: medium description: Searches for the pattern /.git/config on passed URLs. reference: https://www.acunetix.com/vulnerabilities/web/git-repository-found/ tags: git,config
Actual requests and corresponding matchers are placed below the info block and they perform the task of making requests to target servers and finding if the template request was successful.
Each template file can contain multiple requests to be made. The template is iterated and one by one the desired requests are made to the target sites.
The best part of this is you can simply share your crafted template with your team mates, triage/security team to replicate the issue on the other side with ease.