Posts Tagged ‘databases

Can a fingerprint image be reconstructed from the template?

We have ideas that minutiae information is personal and sufficient to identify an individual, and interoperable among different databases, this question becomes less important. However, since many proponents of biometric systems make a claim that a fingerprint image cannot be reconstructed from a minutiae template, we will address this issue.

Until recently, the view of non-reconstruction was dominant in the biometrics community. However, over the last few years, several scientific works were published that showed that a fingerprint can, in fact, be reconstructed from a minutiae template. The most advanced work was published in 2007 by Cappelli. The authors analyzed templates compatible with the ISO/IEC 19794-2 minutiae standard. In one test, they used basic minutiae information only (i.e. positions x, positions y, and directions). In another test, they also used optional information: minutiae types, Core and Delta data, and proprietary data (the ridge orientation field in this case). In all the tests, the authors were able to reconstruct a fingerprint image from the minutiae template. Very often, the reconstructed image had a striking resemblance with the original image. Even though this reconstruction was only approximate, the reconstructed image was sufficient to obtain a positive match in more than 90% of cases for most minutiae matchers.

The potential repercussions of this work for the security and privacy of fingerprint minutiae systems are as follows:

  1. The fingerprint image reconstructed from the minutiae template, known as a “masquerade” image since it is not an exact copy of the original image, will likely fool the system if it is submitted.
  2. A masquerade image can be submitted to the system by injecting it in a digital form after the fingerprint sensor.
  3. A malicious agent could also create a fake fingerprint and physically submit it to the sensor. The techniques of creating a fake fingerprint are inexpensive and well-known from the literature.
  4. The ability to create a masquerade image will increase the level of interoperability for the minutiae template. The masquerade image can be submitted to any other fingerprint system that requires an image (rather than a minutiae template) as an input. No format conversion of the minutiae template would be required. Moreover, the minutiae template can be made compatible even with a non-minutiae fingerprint system (these systems are rare, however).

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Analysis of the index data model from a databases perspective

The logical representation of indexes is an abstraction for their actual physical implementation(e.g. inverted indexes, suffix trees, suffix arrays or signature files). This abstraction resembles the data independence principle exploited by databases and, by further investigation, it appears clear how databases and search engine indexes have some similarities in the nature of their data structures: in the relational model we refer to a table as a collection of rows having a uniform structure and intended meaning; a table is composed by a set of columns, called attributes, having values taken from a set of domains (like integers, string or boolean values). Likewise, in the index data model, we refer to an index as a collection of documents of a given (possibly generic) type having uniform structure and intended meaning where a document is composed of a (possibly unitary) set of fields having values also belonging to different domains (string, date, integer etc).

Differently from the databases, though, search engine indexes do not have functional dependencies nor inclusion dependencies defined for their fields, except for an implied key dependency used to uniquely identify documents into an index. Moreover, it is not possible to define join dependencies between fields belonging to different indexes. Another difference enlarging the gap between the database data model and the index data model is the lack of standard data definition and data manipulation languages. For example both in literature and in industry there is no standard query language convention (such as SQL for databases) for search engines; this heterogeneity is mainly due to a high dependency of the adopted query convention to the structure and to the nature of the items in the indexed collection.

In its simplest form, for a collection of items with textual representation, a query is composed of keywords and the items retrieved contain these keywords. An extension of this simple querying mechanism is the case of a collection of structured text documents, where the use of index fields allows users to search not only in the whole document but also in its specific attributes. From a database model perspective, though, just selection and projection operators are available: users can specify keyword-based queries over fields belonging to the document structure and, possibly, only a subset of all the fields in the document can be shown as result.

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Privilege Elevation via SQL Injection

Most organizations are familiar with the risk posed by SQL injection in web applications, but fewer are aware of the implications of SQL injection in stored procedures. Any component that dynamically creates and executes a SQL query could in theory be subject to SQL injection. In those databases where mechanisms exist to dynamically compose and execute strings, SQL injection in stored procedures can pose a risk.

In Oracle, for example, stored procedures can execute with either the privilege of the invoker of the procedure, or the definer of the procedure. If the definer was a high-privileged account, and the procedure contains a SQL injection flaw, attackers can use the flaw to execute statements at a higher level of privilege than they should be able to. The following procedures all allow privilege elevation in one form or another:

The DRILOAD.VALIDATE_STMT procedure is especially interesting since no “SQL injection” is really necessary; the procedure simply executes the specified statement with DBA privileges, and the procedure can be called by anyone,for example the default user “SCOTT” can execute the following:


This will grant the “public” role DBA privileges.

In most other databases the effect of SQL injection in stored procedures is less dramatic — in Sybase, for example, “definer rights” immediately back down to “invoker rights” as soon as a stored procedure attempts to execute a dynamically created SQL statement. The same is true of Microsoft SQL Server.

It isn’t true to say that SQL injection in stored procedures has no effect in SQL Server, however — if an attacker can inject SQL into a stored procedure,he can directly modify the system catalog — but only if he already had permissions that would enable him to do so. The additional risk posed by this is slight, since the attacker would already have to be an administrator in order to take advantage of any SQL injection flaw in this way — and if he is a database administrator, there are many other, far more serious things he can do to the system.

One privilege elevation issue in SQL Server is related to the mechanism used to add jobs to be executed by the SQL Server Agent (#NISR15002002B).Essentially, all users were permitted to add jobs, and those jobs would then be executed with the privileges of the SQL Agent itself (by getting the SQL Agent to re-authenticate after it had dropped its privileges).

In general, patching is the answer to this class of problem. In the specific case of Oracle, it might be worth investigating which sets of default stored procedures you actually need in your environment and revoking access to“public” — but as we previously noted, this can cause permission problems that are hard to debug.

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Authentication in ColdFusion

ColdFusion features built-in server-side file search, Adobe Flash and Adobe Flex application connectivity, web services publishing, and charting capabilities. ColdFusion is implemented on the Java platform and uses a Java 2 Enterprise Edition (J2EE) application server for many of  its runtime services. ColdFusion can be configured to use an embedded J2EE server (Adobe JRun), or it can be deployed as a J2EE application on a third party J2EE application server such as Apache Tomcat, IBM WebSphere, and BEA WebLogic.


Web and application server authentication can be thought of as two different controls (see Figure 1). Web server authentication is controlled by the web server administration console or configuration files. These controls do not need to interact with the application code to function. For example, using Apache, you modify the http.conf or .htaccess files; or for IIS, use the IIS Microsoft Management Console. Basic authentication works by sending a challenge request back to a user’s browser consisting of the protected URI. The user must then respond with the user ID and password, separated by a single colon, and encoded using base64 encoding. Application-level authentication occurs at a layer after the web server access controls have been processed. This section examines how to use ColdFusion to authenticate and authorize users to resources at the application level.

Figure 1: Web server and application server authentication occur in sequence before accessis granted to protected resources.

ColdFusion enables you to authenticate against multiple system types. These types include LDAP, text files, Databases, NTLM, Client-Side certificates via LDAP, and others via custom modules. The section below describes using these credential stores according to best practices.

Best practices

  1. applicationTimeout = #CreateTimeSpan(0,8,0,0)#
  2. loginStorage = session
  3. sessionTimeout = #CreateTimeSpan(0,0,20,0)#
  4. sessionManagement = True
  5. scriptProtect = All
  6. setClientCookies = False (Use JSESSIONID)
  7. setDomainCookies = False
  8. name (This value is application-dependent; however, it should be set)

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Blind XPath Injuction

Blind XPath Injection attack that enables an attacker to extract a complete XML document used for XPath querying, without prior knowledge of the XPath query. The attack is considered “complete” since all possible data is exposed. The attack makes use of two techniques –XPath crawling and Booleanization of XPath queries. Using this attack, it is possible to get hold of theXML “database” used in the Xpath query. This can be most powerful against sites that use XPath queries (and XML “databases”) for authentication, searching and other uses.

Compared to the SQL injection attacks, XPath Injection has the following upsides:

1. Since XPath is a standard (yet rich) language, it is possible to carry the attack ‘as-is’ for any XPath implementation. This is in contrast to SQL injection where different implementations have different SQL dialects (there is a common SQL language, but it is often too weak).

2. The XPath language can reference almost all parts of the XML document without access control restrictions, whereas with SQL, a “user” (which is a term undefined in the XPath/XML context) may be restricted to certain tables, columns or queries. So the outcome of the Blind XPath Injection attack is guaranteed to consist of the complete XML document, i.e. the complete database.

It is possible to take a more systematic approach to the XPath Injection problem. This approach is called “blind injection” (the foundations of which are laid in, in the SQL injection context). It assumes more or less nothing on the structure of the query except that the user data is injected in a Boolean expression context. It enables the attacker to extract a single bit of  information per a single query injection. This bit is realized, for example, as “Login successful” or “Login failed”.

This approach is even more powerful with XPath than it is with SQL, due to the following characteristics of XPath:

The technique we use is as follows:

We first show how to crawl an XPath document, using only scalar queries (that is, queries whose return type is “string”, “numeric” or “Boolean”). The crawling procedure assumes no knowledge of the document structure; yet at its end, the document, in its completeness, is reconstructed.

We then show how a scalar XPath query can be replaced by a series of  Boolean queries. This procedure is called a “Booleanization” of the query. A Boolean query is a query whose result is a Boolean value (true/false). So in a Booleanization process, a query whose result type is string or numeric is replaced with a series of queries whose result type is Boolean, and from which we can reconstruct the result ofthe original string or numeric query.

Finally, each Boolean query can be resolved by a single “blind” injection. That is, we show how it is possible to form an injection string, including the Boolean query, that when injected into an XPath query, causes the application to behave in one way if the Boolean query resolves into “true”, and in another way if the query resolves into “false”. This way, the attacker can determine a single bit – the Boolean query result.

The novelty in this approach towards XPath Injection is that it does not require much prior knowledge of the XPath query format, unlike the “traditional” approach described above. It does not require that data from the XML document be embedded in the response and that the whole XML document is eventually extracted, regardless of the format of the XPath query used by the application. It uses only a difference in the application behavior resulting from a difference in the XPath query return value to extract a single information bit.


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