Abstract:
System and method for accurately determining security policy for an application based on dynamic code analysis of application runtime execution(s). A dynamic recorder, dynamic code analyzer and security policy analyzer can evaluate and determine the security decisions and access to secure resources made during a security event within one or more executions of an application in order to identify an existing security policy that best matches an application&#39;s security needs. Security events may be analyzed to determine which security decisions and access to secure resources are necessary and which can be eliminated or replaced with alternative decisions or resources.

Description:
FIELD OF INVENTION 
       [0001]    The present invention is a computer implemented dynamic code analyzer for accurately determining “perfect-fit” and/or “best-fit” security policies that define an application runtime. 
       BACKGROUND 
       [0002]    Development of computer applications usually involves evaluating potential security issues before application code is made available to customers. Static code analyzers have been used to check for these security issues. Static code checkers check that coding standards are upheld, and mark code that is potentially harmful and thus likely to be more error prone. Harmful code may be an unprotected sequence of code leading to program vulnerabilities. A Static Code Analyzer can help developers detect coding and security related issues earlier in the development cycle thereby reducing the overall cost of fixing code defects. 
         [0003]    Many computer-implemented applications require access to external resources (e.g. data files, access to the Internet) in order to execute properly. Evidence from the application (e.g., code characteristics) presented at runtime can determine which security policy should control the application&#39;s access to external resources and other security related issues. The evidence is based either on the code identity, such as code characteristics including among other things, digital signature, application directory, hash, publisher, site of origin, URL of origin, zone of origin, and/or with custom supplied evidences. Once a security policy is selected, a security manager can enforce the policy when executing the application. 
         [0004]    Current implementations are ineffective because static code analyzers easily overestimate the required permissions for access to external resources (e.g., shared code between applications) because they consider the whole application (e.g., one time initialization, administrative options) and not the parts that are really being executed by the end user. Thus static analyzers are not able to identify the best security policy target for an application. Inaccurate security permissions may result in application code unnecessarily being allowed permissions and access to secure resources (e.g., granting too much permission). This is especially a concern when many applications run in highly secure environments, where the permissions should be as minimal as possible. There exists a need for limiting software application permissions more accurately and effectively. 
       SUMMARY OF THE INVENTION 
       [0005]    Various aspects of the invention overcome at least some of these and other drawbacks of known systems. According to one embodiment of the invention, a system and method provides dynamic code analysis for logged execution data, identifying security related events from the logged execution data, and determining a security policy that corresponds to the identified security related events of the execution. This may be referred to as a “perfect fit” security policy. 
         [0006]    According to another aspect of the invention, the identified perfect-fit security policy can be compared to existing security policies including system defaults in order to identify a minimal superset to the perfect fit security policy from the existing security policies. This superset may be referred to as a “best-fit” security policy, which allows the application to run as normal and avoids having to create excess security policies that need to be managed. 
         [0007]    According to another aspect of the invention, a system may be used for further determining whether security permission(s) may be replaced with more restrictive security permission(s) without affecting the applications functions. Changes may be determined by analyzing the recorded logs associated with the original security permission(s). This determination may result in a list of suggested security changes for the running application. These suggested changes, which may be implemented by modifying the application source code, can be put through the same process (for a single or for multiple iterations), which will yield a more accurate and secure security policy. Therefore, modification to the application source code can result in a different set of permissions to execute with the same or very similar results. 
         [0008]    The system and method of the invention allows more effective and accurate assessment of application security requirements. This allows the selection of the best existing policy or, if required, to build a custom security policy for the application. More restrictive security policies may be associated with the application while still allowing the application to continue to work properly without unnecessarily exposing secure resources. 
         [0009]    These and other objects, features and advantages of the invention will be apparent through the detailed description of the embodiments and the drawings attached hereto. It is also to be understood that both the foregoing general description and the following detailed description are exemplary and not restrictive of the scope of the invention. 
     
     
       DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a high-level block diagram, according to an embodiment of the invention. 
           [0011]      FIG. 2  is a flow diagram according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The present invention offers a method for obtaining more accurate information about the security permissions required by an application to run. The required permissions to execute properly are a subset of the all the permissions that can be required by the application (e.g. setup code, configuration, administrative tasks). Analysis on dynamically recorded application execution data can identify the executed permissions and the context in which they are executed. In comparison, a static analysis will detect, indiscriminately, all permissions and, even then, misses the permission required if some code is loaded dynamically. The gathered information (i.e. evidences, permissions, context) can be used to determine an application specific security policy or the best match to a pre-existing security policy. As such, many factors may be considered in assigning a security policy. A security policy may be characteristic of the permissions that an application is allowed to have. A permission set and security policy may be determined based on various factors of the application&#39;s runtime. 
         [0013]      FIG. 1  is a high-level block diagram of an exemplary system for a method of the invention. One or more applications may be presented for execution on a computer  10 . Application code ( 12 ,  14 ) may be downloaded to a computer  10  through a network connection. Other application sources may be included (e.g., hard disk, CD, drive storage). Thus, application code ( 12 ,  14 ) on a computer  10  may originate from various sources that are either secure, un-secure, or semi-secure. 
         [0014]    Execution of applications may be carried out using a runtime module  16  (e.g., Common Language Runtime, ECMA runtime, etc.). Code Access Security (CAS)  18  allows the runtime module  16  to restrict the permissions allowed to an application based on the applicable security policy or policies. Runtime module  16  and CAS  18  are generally known in the art. A novel aspect of the system includes the dynamic recorder  28 , records database  32 , dynamic code analyzer  20  and the security policy module  22 . A dynamic recorder  28  may dynamically record permission related data (e.g., access requests, edit, write, store, delete permissions), context related data, and evidence related data that occurs during application code execution to a records database  32 . Multiple execution instances may be recorded in order to analyze the application more completely. Database  32 , or other location, may store dynamically record data from application execution runtime. The application execution data may include, but is not limited to, information from each resource the application invoked during execution including permission checks (e.g., Link, Inheritance and Demand); the data used in the security decision process (e.g. stack); and the results (e.g., success or failure); the evidence of the executing code, the XML representation of the requested permissions; access to secure resources  24  including shared directories  26 , assembly cache  25 , and/or code libraries  27 . Resource access to other sources may also exist. The recorded data may be characterized into events and recorded for further analysis. The data may be sent to a remote location if desired. 
         [0015]    The dynamic code analyzer  20  and the security policy module  22  interpret the recorded data. The dynamic code analyzer  20  may parse the dynamically collected data to identify various security and/or other observed events. The dynamic code analyzer  20  may also interpret the recorded permissions, among other things, into useful information regarding security. Security policy module  22  may further process the information from the dynamic code analyzer  20  to determine a minimal security policy for executing the application. A minimal security policy may be defined by the most restrictive security policy that still allows the application to execute normally. The security policy module  22  may create a minimal security policy using one or a combination of implementations including perfect fit, best fit and incorporating suggested changes. Information regarding a created security policy and/or previously created security policy (e.g., existing security policies) may be stored at security policies database  30 , or other location. 
         [0016]    A perfect fit security policy may utilize a dynamic code analyzer  20  to analyze logged execution data. The dynamically recorded execution(s) may be analyzed to identify one or more security related events associated with application execution. A security policy module  22  may create a security policy corresponding to the identified one or more security related events of the recorded execution. Thus, the perfect fit security policy is determined based on each applications unique execution events. 
         [0017]    A best fit security policy may be determined based on comparing and matching a pre-existing security policy to the recorded execution and/or the determined perfect fit security policy. For example, a perfect fit security policy may be compared with existing policies, including system defaults, in order to identify an existing policy that provides a minimal superset to the perfect fit policy. This allows the application to be matched to an existing policy without limiting any functions of the application and avoids having to create an entirely new security policy for each application which in turn the computer system has to store and manage. If the only matching existing security policy is found to be a security policy with the least secure permissions as compared with other existing policies (e.g., Full Trust), than a match may not be recognized. This may allow the creation of a new security policy to be established having greater permissions than the least secure permissions policy but less than or equal to the permissions required. In essence, the new policy may be created between the two. However, in same cases the policy with the least secure permissions may be used a a valid minimal superset. 
         [0018]    Even after the matching process it is still possible to have a suboptimal security policy (e.g. the perfect-fit policy requires too many permissions or the best-fit policy allows too many permissions). To further change the security policy may require a change to the permissions themselves. This may not be done directly as the permissions are requested by the events generated by the applications. However, the events themselves can be analyzed and alternative programming solutions, leading to similar events but with different security requirements, can be suggested (e.g., suggesting the use of isolated storage instead of the normal file based storage). Determination of alternatives may result in a list of suggested security changes for the running application. Once the suggested changes are applied to the application (by making changes to the source code) the whole process can be started again. The suggested changes, if implemented, will yield a more accurate and secure security policy when combined with the perfect fit policy or identified best fit security policy. It is possible, but not necessary, to iterate this process several times until no more changes can be applied to the application source code. 
         [0019]    Alternatively, more restrictive security permissions may be selected that do limit the applications functions, but do not render the application fully unusable. For example, an application which results in incoming access to secure resources  24  from an outside source (e.g. the Internet) may be prevented, while outgoing access from the computer  10  may still be allowed. Thus an application may have limited ability without disabling all application capabilities. 
         [0020]      FIG. 2  is a flow diagram that illustrates a method of the invention according to an embodiment of the invention. At runtime execution an application may proceed to execute on the computer  10  (operation  50 ). During application runtime execution, data associated with the actions and events of application runtime execution are recorded and stored (operation  52  and  54 ). At operation  56 , analysis may include parsing the data from one or more application runtime execution instances. The security events and/or other runtime actions may be identified in analysis, which may be carried out to varying degrees. Information about the identified events, particularly security events, may be further processed to determine a security policy (operation  58 ). In operation  60 , a perfect fit security policy may be determined. The perfect fit security policy may be matched with one or more existing security policies (operation  62 ). A match may be determined based on whether an existing security policy is a superset of the determined perfect fit security policy. The matching existing policy that is the minimal superset (e.g., the superset the closest to the perfect-fit policy), is identified as the best fit policy for which the application gets assigned (operation  64 ). However, if the superset is too large, (e.g., too few permissions) then a good match may not be recognized. Operation  66  may identify, based on logged runtime data (e.g., security events), possible changes to the application that, if implemented, would reduce the security requirements for executing the application, without affecting its capabilities. For example, alternative suggestions may include, using Isolated Storage versus normal file access; accessing “safe” intranet resources instead of similar public internet resources; using managed resources instead of invoking native code and/or; asserting certain permissions that are know to be safe in the particular context. Furthermore, upon analysis, if a permission request is found to be unnecessary it may be eliminated. 
         [0021]    The alternatives may be suggested to the user so that a developer (or other entity) may determine whether it is possible to incorporate one or more of them into the application (operation  68 ). If so, the method may return to operation  50  and restart analyzing the new application with all, or some of, the suggested changes. Such iterations may be done multiple times for an application until there is no more changes judged acceptable to the developer. Otherwise, a new security policy may be created and stored for use with the application (operation  70 ). For subsequent processing of application security policies, the security policy created in operation  70  may be referred to as an existing security policy. 
         [0022]    Thus, the method described may be used to determine whether an application can properly execute using reduced permissions. This allows permissions to be mapped into the existing policy that best fits the permissions set needed for an application to run successfully. Also based on information logged and evaluated using a dynamic recorder  28 , dynamic code analyzer  20  and security policy module  22  an accurate specific security policy may be created for the application and stored at security policy database  30 . Thus, the system and method of the invention provides a less complex method for managing security policies while providing a more accurate security policy for applications. 
         [0023]    In the foregoing specification, the invention has been described with reference to specific embodiments thereof. Various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.