XnLinkFinder v4.1 – A Comprehensive Guide To Discovering Endpoints And Parameters

This is a tool used to discover endpoints (and potential parameters) for a given target. It can find them by:

crawling a target (pass a domain/URL)
crawling multiple targets (pass a file of domains/URLs)
searching files in a given directory (pass a directory name)
get them from a Burp project (pass location of a Burp XML file)
get them from an OWASP ZAP project (pass location of a ZAP ASCII message file)
get them from a Caido project (pass location of a Caido export CSV file)
processing a waymore results directory (searching archived response files from waymore -mode R and also requesting URLs from waymore.txt and the original URLs from index.txt – see waymore README.md)

The python script is based on the link finding capabilities of my Burp extension GAP. As a starting point, I took the amazing tool LinkFinder by Gerben Javado, and used the Regex for finding links, but with additional improvements to find even more.

Installation

xnLinkFinder supports Python 3.

$ git clone https://github.com/xnl-h4ck3r/xnLinkFinder.git
$ cd xnLinkFinder
$ sudo python setup.py install

Usage

Arg	Long Arg	Description
-i	–input	Input a: URL, text file of URLs, a Directory of files to search, a Burp XML output file, an OWASP ZAP output file, or a Caido CSV file.
-o	–output	The file to save the Links output to, including path if necessary (default: output.txt). If set to `cli` then output is only written to STDOUT. If the file already exist it will just be appended to (and de-duplicated) unless option `-ow` is passed.
-op	–output-params	The file to save the Potential Parameters output to, including path if necessary (default: parameters.txt). If set to `cli` then output is only written to STDOUT (but not piped to another program). If the file already exist it will just be appended to (and de-duplicated) unless option `-ow` is passed.
-owl	–output-wordlist	The file to save the target specific Wordlist output to, including path if necessary (default: No wordlist output). If set to `cli` then output is only written to STDOUT (but not piped to another program). If the file already exist it will just be appended to (and de-duplicated) unless option -ow is passed.
-ow	–output-overwrite	If the output file already exists, it will be overwritten instead of being appended to.
-sp	–scope-prefix	Any links found starting with `/` will be prefixed with scope domains in the output instead of the original link. If the passed value is a valid file name, that file will be used, otherwise the string literal will be used.
-spo	–scope-prefix-original	If argument `-sp` is passed, then this determines whether the original link starting with `/` is also included in the output (default: false)
-spkf	–scope-prefix-keep-failed	If argument `-spkf` is passed, then this determines whether a prefixed link will be kept in the output if it was a 404 or a RequestException occurs (default: false)
-sf	–scope-filter	Will filter output links to only include them if the domain of the link is in the scope specified. If the passed value is a valid file name, that file will be used, otherwise the string literal will be used. This argument is now mandatory if input is a domain/URL (or file of domains/URLs) to prevent crawling sites that are not in scope and also preventing misleading results.
-c	–cookies †	Add cookies to pass with HTTP requests. Pass in the format `'name1=value1; name2=value2;'`
-H	–headers †	Add custom headers to pass with HTTP requests. Pass in the format `'Header1: value1; Header2: value2;'`
-ra	–regex-after	RegEx for filtering purposes against found endpoints before output (e.g. `/api/v[0-9]\.[0-9]\*` ). If it matches, the link is output.
-d	–depth †	The level of depth to search. For example, if a value of 2 is passed, then all links initially found will then be searched for more links (default: 1). This option is ignored for Burp files, ZAP files and Caido files because they can be huge and consume lots of memory. It is also advisable to use the `-sp` (`--scope-prefix`) argument to ensure a request to links found without a domain can be attempted.
-p	–processes †	Basic multithreading is done when getting requests for a URL, or file of URLs (not a Burp file, ZAP file or Caido file). This argument determines the number of processes (threads) used (default: 25)
-x	–exclude	Additional Link exclusions (to the list in `config.yml`) in a comma separated list, e.g. `careers,forum`
-orig	–origin	Whether you want the origin of the link to be in the output. Displayed as `LINK-URL [ORIGIN-URL]` in the output (default: false)
-prefixed		Whether you want to see which links were prefixed in the output. Displays `(PREFIXED)` after link and origin in the output (default: false)
-xrel	–exclude-relative-links	By default, if any links in the results start with `./` or `../`, they will be included. If this argument is used, these relative links will not be added.
-t	–timeout †	How many seconds to wait for the server to send data before giving up (default: 10 seconds)
-inc	–include	Include input (`-i`) links in the output (default: false)
-u	–user-agent †	What User Agents to get links for, e.g. `-u desktop mobile`
-insecure	†	Whether TLS certificate checks should be disabled when making requests (delfault: false)
-s429	†	Stop when > 95 percent of responses return 429 Too Many Requests (default: false)
-s403	†	Stop when > 95 percent of responses return 403 Forbidden (default: false)
-sTO	†	Stop when > 95 percent of requests time out (default: false)
-sCE	†	Stop when > 95 percent of requests have connection errors (default: false)
-m	–memory-threshold	The memory threshold percentage. If the machines memory goes above the threshold, the program will be stopped and ended gracefully before running out of memory (default: 95)
-mfs	–max-file-size †	The maximum file size (in bytes) of a file to be checked if -i is a directory. If the file size os over, it will be ignored (default: 500 MB). Setting to 0 means no files will be ignored, regardless of size.
-rp	–replay-proxy†	For active link finding with URL (or file of URLs), replay the requests through this proxy.
-ascii-only		Whether links and parameters will only be added if they only contain ASCII characters. This can be useful when you know the target is likely to use ASCII characters and you also get a number of false positives from binary files for some reason.
-mtl	–max-time-limit	The maximum time limit (in minutes) to run before stopping (default: 0). If 0 is passed, there is no limit.
	–config	Path to the YML config file. If not passed, it looks for file `config.yml` in the same directory as runtime file `xnLinkFinder.py`
-nwlpl	–no-wordlist-plurals	When words are found for a target specific wordlist, by default new words are added if there is a singular word from a plural, and vice versa. If this argument is used, this process is not done.
-nwlpw	–no-wordlist-pathwords	By default, any path words found in the links will be processed for the target specific wordlist. If this argument is used, they will not be processed. NOTE: if the YAML config value of `respParamPathWords` is `True` then this argument will not have any effect unless `-nwlpm`/`--no-wordlist-parameters` is also passed.
-nwlpm	–no-wordlist-parameters	By default, any parameters found in the links will be processed for the target specific wordlist. If this argument is used, they will not be processed.
-nwlc	–no-wordlist-comments	By default, any comments in pages will be processed for the target specific wordlist. If this argument is used, they will not be processed.
-nwlia	–no-wordlist-imgalt	By default, any image ‘alt’ attributes will be processed for the target specific wordlist. If this argument is used, they will not be processed.
-nwld	–no-wordlist-digits	Exclude any words from the target specific wordlist with numerical digits in.
-nwll	–no-wordlist-lowercase	By default, any word added with any uppercase characters in will also add the word in lowercase. If this argument is used, the lowercase words will not be added.
-wlml	–wordlist-maxlen	The maximum length of words to add to the target specific wordlist, excluding plurals (default: 0 – no limit)
-swf	–stopwords-file	A file of additional Stop Words (in addition to “stopWords” in the YML Config file) used to exclude words from the target specific wordlist. Stop Words are used in Natural Language Processing and different lists can be found in different libraries. You may want to add words in different languages, depending on your target.
-nb	–no-banner	Hides the tool banner.
-v	–verbose	Verbose output
-vv	–vverbose	Increased verbose output
	–version	Show current version number.
-h	–help	show the help message and exit

† NOT RELEVANT FOR INPUT OF DIRECTORY, BURP XML FILE, OWASP ZAP FILE OR CAIDO CSV FILE

config.yml

The config.yml file has the keys which can be updated to suit your needs:

linkExclude – A comma separated list of strings (e.g. .css,.jpg,.jpeg etc.) that all links are checked against. If a link includes any of the strings then it will be excluded from the output. If the input is a directory, then file names are checked against this list.
contentExclude – A comma separated list of strings (e.g. text/css,image/jpeg,image/jpg etc.) that all responses Content-Type headers are checked against. Any responses with the these content types will be excluded and not checked for links.
fileExtExclude – A comma separated list of strings (e.g. .zip,.gz,.tar etc.) that all files in Directory mode are checked against. If a file has one of those extensions it will not be searched for links. Also, in normal mode, if a response doesn’t have a content-type to check for exclusions, it will check for these extensions at the end of the URL to determine if to search for links.
regexFiles – A list of file types separated by a pipe character (e.g. php|php3|php5 etc.). These are used in the Link Finding Regex when there are findings that aren’t obvious links, but are interesting file types that you want to pick out. If you add to this list, ensure you escape any dots to ensure correct regex, e.g. js\.map
respParamLinksFound † – Whether to get potential parameters from links found in responses: True or False
respParamPathWords † – Whether to add path words in retrieved links as potential parameters: True or False
respParamJSON † – If the MIME type of the response contains JSON, whether to add JSON Key values as potential parameters: True or False
respParamJSVars † – Whether javascript variables set with var, let or const are added as potential parameters: True or False
respParamXML † – If the MIME type of the response contains XML, whether to add XML attributes values as potential parameters: True or False
respParamInputField † – If the MIME type of the response contains HTML, whether to add NAME and ID attributes of any INPUT fields as potential parameters: True or False
respParamMetaName † – If the MIME type of the response contains HTML, whether to add NAME attributes of any META tags as potential parameters: True or False
wordsContentTypes – A comma separated list of strings (e.g. text/html,text/plain) to specify which response content types will be searched for words to go in the target specific wordlist.
stopWords – A comma separated list of strings (e.g. then,this,that) to specify words that are excluded from the target specific wordlist. This default list is initially made up of English determiners, coordinating conjuctions and prepositions, plus a list of stop words from Scikit-Learn, a python machine learning library.

† IF THESE ARE NOT FOUND IN THE CONFIG FILE THEY WILL DEFAULT TO True

Examples

Find Links From A Specific Target – Basic

python3 xnLinkFinder.py -i target.com -sf target.com

Find Links From A Specific Target – Detailed

Ideally, provide scope prefix (-sp) with the primary domain (including schema), and a scope filter (-sf) to filter the results only to relevant domains (this can be a file or in scope domains). Also, you can pass cookies and customer headers to ensure you find links only available to authorised users. Specifying the User Agent (-u desktop mobile) will first search for all links using desktop User Agents, and then try again using mobile user agents. There could be specific endpoints that are related to the user agent given. Giving a depth value (-d) will keep sending request to links found on the previous depth search to find more links.

python3 xnLinkFinder.py -i target.com -sp target_prefix.txt -sf target_scope.txt -spo -inc -vv -H 'Authorization: Bearer XXXXXXXXXXXXXX' -c 'SessionId=MYSESSIONID' -u desktop mobile -d 10

Find Links from a list of URLs – Basic

If you have a file of JS file URLs for example, you can look for links in those:

python3 xnLinkFinder.py -i target_js.txt -sf target.com

Find Links From A Files In A Directory – Basic

If you have a files, e.g. JS files, HTTP responses, etc. you can look for links in those:

python3 xnLinkFinder.py -i ~/Tools/waymore/results/target.com

NOTE: Sub directories are also checked. The -mfs option can be specified to skip files over a certain size.

Find Links From A Burp Project – Basic

In Burp, select the items you want to search by highlighting the scope for example, right clicking and selecting the Save selected items. Ensure that the option base64-encode requests and responses option is checked before saving. To get all links from the file (even with HUGE files, you’ll be able to get all the links):

python3 xnLinkFinder.py -i target_burp.xml

NOTE: xnLinkFinder makes the assumption that if the first line of the file passed with -i starts with <?xml then you are trying to process a Burp file.

Find Links From A Burp Project – Detailed

Ideally, provide scope prefix (-sp) with the primary domain (including schema), and a scope filter (-sf) to filter the results only to relevant domains.

python3 xnLinkFinder.py -i target_burp.xml -o target_burp.txt -sp https://www.target.com -sf target.* -ow -spo -inc -vv

Find Links from an OWASP ZAP project – Basic

In ZAP, select the items you want to search by highlighting the History for example, clicking menu Export and selecting Export Messages to File.... This will let you save an ASCII text file of all requests and responses you want to search. To get all links from the file (even with HUGE files, you’ll be able to get all the links):

python3 xnLinkFinder.py -i target_zap.txt

NOTE: xnLinkFinder makes the assumption that if the first line of the file passed with -i is in the format ==== 99 ========== (v2.11.1) or ===99 ========== (v2.12) for example, then you are trying to process an OWASP ZAP ASCII text file.

Find Links From A Cadio Export CSV File – Basic

In Caido, go to the History section and select the Export option.

If you are using Caido Pro or Enterprise edition, then choose the Export current rows option and pick As CSV. Go to the Exports section and download the CSV file. Then pass as input:

python3 xnLinkFinder.py -i 2023-03-18-010332_csv_requests.csv

If you are using Caido Community edition, then you will have to choose the Export all option and pick As CSV. Go to the Exports section and download the CSV file. As you have the full history, you will want to remove anything that is not relevant from the CSV file. Use the example below, where redbull is the main part of the domains of the target you are looking at.

cat 2023-03-18-010332_csv_requests.csv | grep -E '^id|^[0-9]+,[^,]*redbull' > caido_redbull.csv
python3 xnLinkFinder.py -i caido_redbull.csv

NOTE: xnLinkFinder makes the assumption that if the first line of the file passed with -i is in the format id,host,method, then you are trying to process a Caido export CSV file.

Find Links From A Waymore Results Directory

The waymore tool can be used to get URLs from various third party APIs, and also download archived responses from archive.org (Wayback Machine). Passing a waymore results directory to xnLinKFinder will search the contents of archived responses, and also request URLs from waymore.txt and also the archived URLs from index.txt and get more links from those responses.

python3 xnLinkFinder.py -i ~/Tools/waymore/results/target.com

NOTE: It is passed as a normal directory, but xnLinkFinder will determine it is a waymore results directory and process respectively. This relies on the default naming convention of the URLs file being waymore.txt and that file being in the same directory as the archived files (which it is by default).

Piping To Other Tools

You can pipe xnLinkFinder to other tools. Any errors are sent to stderr and any links found are sent to stdout. The output file is still created in addition to the links being piped to the next program. However, potential parameters are not piped to the next program, but they are still written to file. For example:

python3 xnLinkFinder.py -i redbull.com -sp https://redbull.com -sf rebbull.* -d 3 | unfurl keys | sort -u

You can also pass the input through stdin instead of -i.

cat redbull_subs.txt | python3 xnLinkFinder.py -sp https://redbull.com -sf rebbull.* -d 3

NOTE: You can’t pipe in a Burp, ZAP or Caido file, these must be passed using -i.

Recommendations And Notes

Always use the Scope Prefix argument -sp. This can be one scope domain, or a file containing multiple scope domains. Below are examples of the format used (no path should be included, and no wildcards used. Schema is optional, but will default to http):

http://www.target.com
https://target-payments.com
https://static.target-cdn.com

If a link is found that has no domain, e.g. /path/to/example.js then giving passing -sp http://www.target.com will result in teh output http://www.target.com/path/to/example.js and if Depth (-d) is >1 then a request will be able to be made to that URL to search for more links. If a file of domains are passed using -sp then the output will include each domain followed by /path/to/example.js and increase the chance of finding more links.
If you use -sp but still want the original link of /path/to/example.js (without a domain) additionally returned in the output, the pass the argument -spo.
Always use the Scope Filter argument -sf. This will ensure that only relevant domains are returned in the output, and more importantly if Depth (-d) is >1 then out of scope targets will not be searched for links or parameters. This can be one scope domain, or a file containing multiple scope domains. Below are examples of the format used (no schema or path should be included):

target.*
target-payments.com
static.target-cdn.com

THIS IS FOR FILTERING THE LINKS DOMAIN ONLY.

If you want to filter the final output in any way, use -ra. It’s always a good idea to use to check your Regex expression is going to do what you expect.
Use the -v option to have a better idea of what the tool is doing.
If you have problems, use the -vv option which may show errors that are occurring, which can possibly be resolved, or you can raise as an issue on github.
Pass cookies (-c), headers (-H) and regex (-ra) values within single quotes, e.g. -ra '/api/v[0-9]\.[0-9]\*'
Set the -o option to give a specific output file name for Links, rather than the default of output.txt. If you plan on running a large depth of searches, start with 2 with option -v to check what is being returned. Then you can increase the Depth, and the new output will be appended to the existing file, unless you pass -ow.
Set the -op option to give a specific output file name for Potential Parameters, rather than the default of parameters.txt. Any output will be appended to the existing file, unless you pass -ow.
If using a high Depth (-d) be wary of some sites using dynamic links so will it will just keep finding new ones. If no new links are being found, then xnlLinkFinder will stop searching. Providing the Stop flags (s429, s403, sTO, sCE) should also be considered.
If you are finding a large number of links (especially if the Depth (-d value is high), and have limited resources, the program will stop when it reaches the memory Threshold (-m) value and end gracefully with data intact before getting killed.
If you decide to cancel xnLinkFinder (using Ctrl-C) in the middle of running, be patient and any gathered data will be saved before ending gracefully.
Using the -orig option will show the URL where the link was found. This can mean you have duplicate links in the output if the same link was found on multiple sources, but it will suffixed with the origin URL in square brackets.
When making requests, xnLinkFinder will use a random User-Agent from the current group, which defaults to desktop. If you have a target that could have different links for different user agent groups, the specify -u desktop mobile for example (separate with a space). The mobile user agent option is an combination of mobile-apple, mobile-android and mobile-windows.
When -i has been set to a directory, the contents of the files in the root of that directory will be searched for links. Files in sub-directories are not searched. Any files that are over the size set by -mfs (default: 500 MB) will be skipped.
When using the -replay-proxy option, sometimes requests can take longer. If you start seeing more Request Timeout errors (you’ll see errors if you use -v or -vv options) then consider using -t to raise the timeout limit.
If you know a target will only have ASCII characters in links and parameters then consider passing -ascii-only. This can eliminate a number of false positives that can sometimes get returned from binary data.
If you pass a waymore results directory, it is worth passing the -d/--depth argument to search any extra links found from URL requests and also the -u/--user-agent if you think there could be different content found, e.g. -u desktop mobile.
Always pass the -owl/--output-wordlist filename to save the target specific wordlist. This list can be very useful when fuzzing a target.
The words for the target specific wordlist are taken from the following sources (any of 3 characters or more), but are also determined by the other wordlist arguments (see Usage section above):
- All responses with certain conditions:
  - Only responses with content types specific in the YML config wordsContentTypes section are searched. The defaults are text/html,application/xml,application/json,text/plain
  - Words from <meta> tag content where:
    - Property is og:title or og:description
    - Name is description,keywords,twitter:title or twitter:description
  - Words from HTML comments
  - Words from alt attribute of <img> tags
  - Words from the rest of the inner HTML of the page, excluding tags <style>, <script> and <link>
- Words found from path words in links found.
- Parameters found from responses and links.
- All valid words will also have the singular/plural version added to the wordlist if possible.
- If the original word has any upper case characters, a lower case version will also be added
If the default “Stop Words” for a target specific wordlist are not good enough, either change in the YML config file, or provide additional stop words using the -swf/--stopwords-file option. You may want to include stop words in another language, depending on the target. Stop words are used in Natural Language Processing (NLP) and many stop word lists can be found online to suit different needs.

Varshini

Tamil has a great interest in the fields of Cyber Security, OSINT, and CTF projects. Currently, he is deeply involved in researching and publishing various security tools with Kali Linux Tutorials, which is quite fascinating.