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Testing for Storing too Much Data in Session (OWASP-DS-008)
This article is part of the OWASP Testing Guide v3. The entire OWASP Testing Guide v3 can be downloaded here.
OWASP at the moment is working at the OWASP Testing Guide v4: you can browse the Guide here
In this test, we check whether it is possible to allocate big amounts of data into a user session object in order to make the server exhaust its memory resources.
Description of the Issue
Care must be taken not to store too much data in a user session object. Storing too much information in the session, such as large quantities of data retrieved from the database, can cause denial of service issues. This problem is exacerbated if the session is populated when serving unauthenticated users, because, in this case, an attacker can launch the attack without having to obtain an account.
Black Box Testing and Examples
This is again a difficult case to test in a pure black box setting. Likely places to look for this vulnerability are those where a large number of records are retrieved from a database, based on data provided by the user during their normal application use. Good candidates may also include paging code, i.e., the functionality of viewing a large record set a portion at a time. The developer may have chosen to cache the records in the session instead of returning to the database for the next block of data. If this is suspected, create a script to automate the creation of many new sessions with the server and run the request that is suspected of caching the data within the session for each one. Let the script run for a while, and then observe the responsiveness of the application for new sessions. It may be possible that a Virtual Machine (VM) or even the server itself will begin to run out of memory because of this attack.
Gray Box Testing and Examples
If available, SNMP can provide information about the memory usage of a machine. Being able to monitor the target memory usage can greatly help when performing this test, as the tester would be able to see what happens when the script described in the previous section is launched.