Engine
To execute the code, a list of language interpreters, which are installed or available on the system environment, is specified. These interpreters can be and not limited tobash
sh
py
python3
, go
, ps
, among others, and they are searched sequentially until a suitable one is found. The identifiers for these interpreters should correspond to their respective names or identifiers recognized by the system environment.
Parts
Validpart
values supported by Code protocol for Matchers / Extractor are -
Value | Description |
---|---|
response | execution output (trailing whitespaces are filtered) |
stderr | Raw Stderr Output(if any) |
Args
Args are arguments that are sent to engine while executing the code. For example if we want to bypass execution policy in powershell for specific template this can be done by adding following args to the template.Pattern
Pattern field can be used to customize name / extension of temporary file while executing a code snippet in a templatepattern: "*.ps1"
will make sure that name of temporary file given pattern.
Below is a example code template where we are executing a powershell script while customizing behaviour of execution policy and setting pattern to *.ps1
Template Signing
Template signing via the private-public key mechanism is a crucial aspect of ensuring the integrity, authenticity and security of templates. This mechanism involves the use of asymmetric cryptography, specifically ECDSA algorithm, to create a secure and verifiable signature. In this process, a template author generates a private key that remains confidential and securely stored. The corresponding public key is then shared with the template consumers. When a template is created or modified, the author signs it using their private key, generating a unique signature that is attached to the template. Template consumers can verify the authenticity and integrity of a signed template by using the author’s public key. By applying the appropriate cryptographic algorithm (ECDSA), they can validate the signature and ensure that the template has not been tampered with since it was signed. This provides a level of trust, as any modifications or unauthorized changes to the template would result in a failed verification process. By employing the private-public key mechanism, template signing adds an additional layer of security and trust to the template ecosystem. It helps establish the identity of the template author and ensures that the templates used in various systems are genuine and have not been altered maliciously. What does signing a template mean? Template signing is a mechanism to ensure the integrity and authenticity of templates. The primary goal is to provide template writers/consumers a way to trust crowdsource/custom templates ensuring that they are not tampered All official nuclei templates include a digital signature in them and are verified by nuclei while loading templates using ProjectDiscovery’s public key shipped with nuclei binary itself. Individuals / Organizations running nuclei in their work environment can generate their own key-pair withnuclei
and sign their custom templates with their private key, thus ensuring that only authorized templates are being used in their environment.
This also allows entities to fully utilize the power of new protocols like code
without worrying about malicious custom templates being used in their environment.
NOTE:
- Template signing is optional for all protocols except
code
. - Unsigned code templates are disabled and can not be executed using nuclei.
- Only signed code templates by the author (yourself) or ProjectDiscovery can be executed.
- Template signing is primarily introduced to ensure security of template to run code on host machine.
- Code file references (ex:
source: protocols/code/pyfile.py
) are allowed and content of these files is included in the template digest. - Payload file references (ex:
payloads: protocols/http/params.txt
) are not included in the template digest as it is treated as a payload/helper and not actual code that is being executed. - Template signing is deterministic while both signing and verifying a template i.e if a code file is referenced in a template that is present outside of templates directory with
-lfa
flag then verification will fail if same template is used without-lfa
flag. (Note this only applies to-lfa
i.e local file access flag only)
Signing Custom Template
Simplest and recommended way to generate key-pair and signing/verfifying templates is to usenuclei
itself.
When Signing a template if key-pair does not exist then nuclei will prompt user to generate a new key-pair with options.
Note: Passphrase is optional and can be left blank when used private key is encrypted with passphrase using PEMCipherAES256 AlgoOnce key-pair is generated, you can sign any custom template using
-sign
flag as shown below.
Note: Every time you make any change in your code template, you need to resign it again to run with nuclei.
Template Digest and Signing Keys
When a template is signed, a digest is generated and added to the template. This digest is a hash of the template content and is used to verify the integrity of the template. If the template is modified after signing, the digest will change, and the signature verification will fail during template loading.signature:fragment
, where the signature is the digital signature of the template used to verify its integrity, and the fragment is metadata generated by MD5 hashing the public key to disable re-signing of code templates not written by you.
The key-pair generated by Nuclei is stored in two files in the $CONFIG/nuclei/keys directory
, where $CONFIG
is the system-specific config directory. The private key is stored in nuclei-user-private-key.pem, which is encrypted with a passphrase if provided. The public key is stored in nuclei-user.crt, which includes the public key and identifier (e.g., user/org name) in a self-signed certificate.
$CONFIG/nuclei/keys
directory on another user’s machine or set the NUCLEI_USER_CERTIFICATE
environment variable to the path or content of the public key.
To use the private key, you can copy it to the $CONFIG/nuclei/keys
directory on another user’s machine or set the NUCLEI_USER_PRIVATE_KEY
environment variable to the path or content of the private key.
HIDE_TEMPLATE_SIG_WARNING
environment variable to true
.
FAQ
Found X unsigned or tampered code template?simple-code.yaml
is a code protocol template which is not signed or content of template has been modified after signing which indicates loss of integrity of template.
If you are template writer then you can go ahead and sign the template using -sign
flag and if you are template consumer then you should carefully examine the template before signing it.
Re-signing code templates are not allowed for security reasons?
re-signing code templates are not allowed for security reasons
comes from the Nuclei engine. This error indicates that a code template initially signed by another user and someone is trying to re-sign it.
This measure was implemented to prevent running untrusted templates unknowingly, which might lead to potential security issues.
When you encounter this error, it suggests that you’re dealing with a template that has been signed by another user Likely, the original signer is not you or the team from projectdiscovery.
By default, Nuclei disallows executing code templates that are signed by anyone other than you or from the public templates provided by projectdiscovery/nuclei-templates.
This is done to prevent potential security abuse using code templates.
To resolve this error:
- Open and thoroughly examine the code template for any modifications.
- Manually remove the existing digest signature from the template.
- Sign the template again.