Heuristic methods used in sqlmap

Heuristic methodsused in sqlmap

Miroslav Štampar

([email protected])

Heuristic methodsused in sqlmap

Miroslav Štampar

([email protected])

FSec – FOI 2013, Varaždin (Croatia) September 19th, 2013 2

Heuristic method

Heuristic (/hjʉˈrɪstɨk/; Greek: “Εὑρίσκω”, “find” or “discover”)

Educational shortcuts to ease the cognitive load of making a decision

Speeding up the process of finding a satisfactory solution

Serve as an aid to learning, discovery and problem solving

Experimental and trial-and-error approachResulting with a solution which is not guaranteed to

be optimal


Heuristic SQL injection checks (1)In some cases DBMS error reporting is enabledDeliberately invalid parameter value is sent (e.g. ())'”(''”')

”SQL error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version...”

Narrowing down tests to only those specific to recognized/parsed DBMS

Automatically extending with DBMS specific tests that would be done (only) on higher level

Switch --smart for finding targets in minutes


Heuristic SQL injection checks (2)



Particularly interesting cases when parameter contains integer value (e.g. id=1)Response is changing with value changed (e.g. id=2)Response is the same for arithmetic operation resulting

in original value (e.g. id=1183-1182)Warning the user that the processed parameter is

most probably prone to SQL injection attack(s)Making user aware to persist in eventual further tests

(to use higher --level/--risk and/or --tamper)



In cases when error reporting is turned offAt least one generic (i.e. non-DBMS dependent) SQL

injection technique is foundSingle request per supported DBMS is being sentUsing form supported by only the targeted one (e.g. id=1 AND (SELECT 0x41597548)=0x41597548) for MySQL)

If getting response as expected, narrowing and/or expanding tests for particular DBMS


Type casting detection (1)

In some cases (preventive) hard type casting (e.g. $id=intval($_REQUEST['id'])) is used

Especially noticeable on integer parameter values (e.g. id=1)

Different responses for different integer values (e.g. id=2)

Same response for appended random string values (e.g. id=1vHxr)

High probability that the type casting is being used (hence, not exploitable)

Warning the user of a potentially futile run


Type casting detection (2)


Length constraining detection (1)

Suhosin ( ) - popular open source PHP patch“...protecting servers and users from known and

unknown flaws in PHP applications and PHP core...”Constraining the length of request parameter values

(e.g. GET values constrained to less than 512 chars)Problematic when longer payloads are used (e.g.

injecting of PHP shell through SELECT..INTO OUTFILE statement)


Length constraining detection (2)

One lengthy payload containing a simple boolean question (e.g. id=1 AND 3182=...3182) is sent right after successful identification of SQL injection


WAF detection/fingeprinting (1)Web Application Firewall (engl. abbr. WAF)“...commonly used mechanism for prevention of

malicious web application attacks...”Modsecurity returns HTTP error code 501 on detected

attackF5 BIG-IP adds its own X-Cnection HTTP header to

the responseGeneric detection (switch --check-waf)Fingeprinting 28 different WAF products (switch

--identify-waf)Sending deliberately suspicious payloads and

checking response(s) for unique characteristics


WAF detection/fingeprinting (2)


False positive detection (1)“...term used for describing a result that indicates

that a given condition is present when it is not...”Another way of saying “mistake”Giving false sense of certainty while in reality there is

nothing exploitable at the other sideEspecially noticeable in boolean-based blind and time-

based blind casesSimple tests are being done after the detection phaseInspecting responses to predetermined boolean

operations (e.g. id=1 AND 95>27)


False positive detection (2)


Delay detection (1)Network latency (or lagging) is the main problem of

time-based blind techniqueFor example, used deliberate delay is 1 sec, normal

response times are >0.5 and <2.0 secs, what we can conclude for 1.5 sec response?

Also, how to recognize delays in hard-queries (e.g. BENCHMARK(5000000,MD5('foobar')))?

Mathematical statistics to the rescueGaussian bell-shaped curve for the normal distribution

is being calculatedEverything inside is considered as “normal”, outside

as “not normal”


Delay detection (2)Everything that's normal (i.e. not deliberately

delayed) should fit under the curveμ(t) represents a mean, while σ(t) represents a

standard deviation of response times99.99% of normal response times fall under the

upper border value μ(t) + 7σ(t)


Delay detection (3)

sqlmap learns what's normal and what's not from non-delay based payload responses (e.g. boolean-based blind)

Also, few dummy requests are done if there is a need for more


Delay detection (4)In case of considerable network latency user is

warned to use as high delay value as possible

On the other hand, if negligible, sqlmap optimizes the delay value (if applicable) to a more appropriate one


Finding number of query fields (1)For successful usage of UNION-based technique,

number of fields has to be knownForemost method used is ORDER BY clauseIf response for an arbitrary large value (e.g. id=1 ORDER BY 9664#) drastically differs from neutral (e.g. id=1 ORDER BY 1#)

sqlmap uses adapted (chunked) binary search


Finding number of query fields (2)If ORDER BY method is not usable, similar approach

is used as in delay detectionConstant field value (e.g. NULL) used across a

(current chunk of) search space in UNION ALL SELECT statement

Searching for the number of fields that, compared to the original response, “sticks out” out of others in a statistical manner

Responses for non-valid number of fields will not much differ from each other

Response for the right number of fields will appear not normal compared to others


Finding number of query fields (3)


Questions?

Heuristic methods used in sqlmap

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