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Skipfish Scanner


Skipfish is an active web application security reconnaissance tool. It prepares an interactive sitemap (blow image) for the targeted site by carrying out a recursive crawl and dictionary-based probes. The resulting map is then annotated with the output from a number of active (but hopefully non-disruptive) security checks. The final report generated by the tool is meant to serve as a foundation for professional web application security assessments.



A number of commercial and open source tools with analogous functionality is readily available (e.g., Nikto, Nessus); stick to the one that suits you best. That said, skipfish tries to address some of the common problems associated with web security scanners. Specific advantages include:


  • High performance: 500+ requests per second against responsive Internet targets, 2000+ requests per second on LAN / MAN networks, and 7000+ requests against local instances have been observed, with a very modest CPU, network, and memory footprint. This can be attributed to:


    • Multiplexing single-thread, fully asynchronous network I/O and data processing model that eliminates memory management, scheduling, and IPC inefficiencies present in some multi-threaded clients.
    • Advanced HTTP/1.1 features such as range requests, content compression, and keep-alive connections, as well as forced response size limiting, to keep network-level overhead in check.
    • Smart response caching and advanced server behavior heuristics are used to minimize unnecessary traffic.
    • Performance-oriented, pure C implementation, including a custom HTTP stack.


  • Ease of use: skipfish is highly adaptive and reliable. The scanner features:


    • Heuristic recognition of obscure path- and query-based parameter handling schemes.
    • Graceful handling of multi-framework sites where certain paths obey a completely different semantics, or are subject to different filtering rules.
    • Automatic wordlist construction based on site content analysis.
    • Probabilistic scanning features to allow periodic, time-bound assessments of arbitrarily complex sites.


  • Well-designed security checks: the tool is meant to provide accurate and meaningful results:


    • Handcrafted dictionaries offer excellent coverage and permit thorough $keyword.$extension testing in a reasonable timeframe.
    • Three-step differential probes are preferred to signature checks for detecting vulnerabilities.
    • Ratproxy-style logic is used to spot subtle security problems: cross-site request forgery, cross-site script inclusion, mixed content, issues MIME- and charset mismatches, incorrect caching directives, etc.
    • Bundled security checks are designed to handle tricky scenarios: stored XSS (path, parameters, headers), blind SQL or XML injection, or blind shell injection.
    • Report post-processing drastically reduces the noise caused by any remaining false positives or server gimmicks by identifying repetitive patterns.


That said, skipfish is not a silver bullet, and may be unsuitable for certain purposes. For example, it does not satisfy most of the requirements outlined in WASC Web Application Security Scanner Evaluation Criteria (some of them on purpose, some out of necessity); and unlike most other projects of this type, it does not come with an extensive database of known vulnerabilities for banner-type checks.


Implemented Tests


A rough list of the security checks offered by the tool is outlined below:


  • High risk flaws (potentially leading to system compromise):


    • Server-side SQL injection (including blind vectors, numerical parameters).
    • Explicit SQL-like syntax in GET or POST parameters.
    • Server-side shell command injection (including blind vectors).
    • Server-side XML / XPath injection (including blind vectors).
    • Format string vulnerabilities.
    • Integer overflow vulnerabilities.
    • Locations accepting HTTP PUT.


  • Medium risk flaws (potentially leading to data compromise):


    • Stored and reflected XSS vectors in document body (minimal JS XSS support present).
    • Stored and reflected XSS vectors via HTTP redirects.
    • Stored and reflected XSS vectors via HTTP header splitting.
    • Directory traversal (including constrained vectors).
    • Assorted file POIs (server-side sources, configs, etc).
    • Attacker-supplied script and CSS inclusion vectors (stored and reflected).
    • External untrusted script and CSS inclusion vectors.
    • Mixed content problems on script and CSS resources (optional).
    • Incorrect or missing MIME types on renderables.
    • Generic MIME types on renderables.
    • Incorrect or missing charsets on renderables.
    • Conflicting MIME / charset info on renderables.
    • Bad caching directives on cookie setting responses.


More information is available from the website at




Note: - This is based on a Fedora Core Install


Download skipfish from:




Install openssl from source this is available from:

Install libidn from source, this is available from:


Note: - RPM installs of these utilities will not work


Amend the skipfish Makefile to include the last three extra directories that openssl and libidn installs files on Fedore Core to otherwise skipfish may not find associated pre-requisite files that are required for the installation:



CFLAGS_GEN = -Wall -funsigned-char -g -ggdb -I/usr/local/include/ \

-I/opt/local/include/ -I/usr/local/ssl/include/ \

-I/usr/lib/ -I/usr/local/ssl/lib/ $(CFLAGS) -D_FORTIFY_SOURCE=0



Possible errors encountered:


Missing lcrypto: /usr/bin/ld: cannot find -lcrypto


Correct with: ln /usr/lib/ /usr/lib/


Missing lssl: /usr/bin/ld: cannot find -lssl


Correct with: ln /usr/lib/ /usr/lib/


Copy the desired dictionary from the dictionaries folder to a new file called skipfish.wl




Usage: ./skipfish [ options ... ] -o output_dir start_url [ start_url2 ... ]


Authentication and access options:


-A user:pass - use specified HTTP authentication credentials

-F host:IP - pretend that 'host' resolves to 'IP'

-C name=val - append a custom cookie to all requests

-H name=val - append a custom HTTP header to all requests

-b (i|f) - use headers consistent with MSIE / Firefox

-N - do not accept any new cookies


Crawl scope options:


-d max_depth - maximum crawl tree depth (16)

-c max_child - maximum children to index per node (1024)

-r r_limit - max total number of requests to send (100000000)

-p crawl% - node and link crawl probability (100%)

-q hex - repeat probabilistic scan with given seed

-I string - only follow URLs matching 'string'

-X string - exclude URLs matching 'string'

-S string - exclude pages containing 'string'

-D domain - crawl cross-site links to another domain

-B domain - trust, but do not crawl, another domain

-O - do not submit any forms

-P - do not parse HTML, etc, to find new links


Reporting options:


-o dir - write output to specified directory (required)

-J - be less noisy about MIME / charset mismatches

-M - log warnings about mixed content

-E - log all HTTP/1.0 / HTTP/1.1 caching intent mismatches

-U - log all external URLs and e-mails seen

-Q - completely suppress duplicate nodes in reports

-u - be quiet, disable realtime progress stats


Dictionary management options:


-W wordlist - load an alternative wordlist (skipfish.wl)

-L - do not auto-learn new keywords for the site

-V - do not update wordlist based on scan results

-Y - do not fuzz extensions in directory brute-force

-R age - purge words hit more than 'age' scans ago

-T name=val - add new form auto-fill rule

-G max_guess - maximum number of keyword guesses to keep (256)

Performance settings:

-g max_conn - max simultaneous TCP connections, global (50)

-m host_conn - max simultaneous connections, per target IP (10)

-f max_fail - max number of consecutive HTTP errors (100)

-t req_tmout - total request response timeout (20 s)

-w rw_tmout - individual network I/O timeout (10 s)

-i idle_tmout - timeout on idle HTTP connections (10 s)

-s s_limit - response size limit (200000 B)


Example syntax:

./skipfish -o output_dir
./skipfish -D -o output_dir
./skipfish -D -o output-dir  - Domain wildcarding
./skipfish -A user:pass -o output_dir


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