Crawling code is the practice of scanning a code base of the review target in question. It is, in effect, looking for key pointers wherein a possible security vulnerability might reside. Certain APIs are related to interfacing to the external world or file IO or user management which are key areas for an attacker to focus on. In crawling code we look for API relating to these areas. We also need to look for business logic areas which may cause security issues, but generally these are bespoke methods which have bespoke names and can not be detected directly, even though we may touch on certain methods due to their relationship with a certain key API.
Also we need to look for common issues relating to a specific language; issues that may not be *security* related but which may affect the stability/availability of the application in the case of extraordinary circumstances. Other issues when performing a code review are areas such a simple copyright notice in order to protect one’s intellectual property.
Crawling code can be done manually or in an automated fashion using automated tools. Tools as simple as grep or wingrep can be used. Other tools are available which would search for key words relating to a specific programming language.
The following sections shall cover the function of crawing code for Java/J2EE, .NET and Classic ASP. This section is best used in conjunction with the transactional analysis section also detailed in this guide.
Searching for Key Indicators
The basis of the code review is to locate and analyse areas of code which may have application security implications. Assuming the code reviewer has a thorough understanding of the code, what it is intended to do, and the context in which it is to be used, firstly one needs to sweep the code base for areas of interest.
This can be done by performing a text search on the code base looking for keywords relating to APIs and functions. Below is a guide for .NET framework 1.1 & 2.0
Searching for Code in .NET
Firstly one needs to be familiar with the tools one can use in order to perform text searching, following this one neesd to know what to look for.
In this section we will assume you have a copy of Visual Studio (VS) .NET at hand. VS has two types of search "Find in Files" and a cmd line tool called Findstr.
The test search tools in XP is not great in my experience and if one has to use this make sure SP2 in installed as it works better. To start off, one should scan thorough the code looking for common patterns or keywords such as "User", "Password", "Pswd", "Key", "Http", etc... This can be done using the "Find in Files" tool in VS or using findstring as follows:
findstr /s /m /i /d:c:\projects\codebase\sec "http" *.*
HTTP Request Strings
Requests from external sources are obviously a key area of a security code review. We need to ensure that all HTTP requests received are data validated for composition, max and min length, and if the data falls with the realms of the parameter white-list. Bottom-line is this is a key area to look at and ensure security is enabled.
Here we are looking for responses to the client. Responses which go unvalidated or which echo external input without data validation are key areas to examine. Many client side attacks result from poor response validation. XSS relies on this somewhat.